Mars

Mars

Overview
Mars is the fourth planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. The planet is named after the Roman
Roman mythology
Roman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...

 god of war, Mars
Mars (mythology)
Mars was the Roman god of war and also an agricultural guardian, a combination characteristic of early Rome. He was second in importance only to Jupiter, and he was the most prominent of the military gods worshipped by the Roman legions...

. It is often described as the "Red Planet", as the iron oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

 prevalent on its surface gives it a reddish appearance
Mars surface color
The apparent color of the Martian surface enabled humans to distinguish it from other planets early in human history and motivated them to weave fables of war in association with Mars. One of its earliest names, Har decher, literally meant "Red One" in Egyptian...

. Mars is a terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...

 with a thin atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

, having surface features reminiscent both of the impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

s of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 and the volcanoes, valleys, deserts, and polar ice caps of Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons.
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Encyclopedia
Mars is the fourth planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. The planet is named after the Roman
Roman mythology
Roman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...

 god of war, Mars
Mars (mythology)
Mars was the Roman god of war and also an agricultural guardian, a combination characteristic of early Rome. He was second in importance only to Jupiter, and he was the most prominent of the military gods worshipped by the Roman legions...

. It is often described as the "Red Planet", as the iron oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

 prevalent on its surface gives it a reddish appearance
Mars surface color
The apparent color of the Martian surface enabled humans to distinguish it from other planets early in human history and motivated them to weave fables of war in association with Mars. One of its earliest names, Har decher, literally meant "Red One" in Egyptian...

. Mars is a terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...

 with a thin atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

, having surface features reminiscent both of the impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

s of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 and the volcanoes, valleys, deserts, and polar ice caps of Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons
Olympus Mons
Olympus Mons is a large volcanic mountain on the planet Mars. At a height of almost , it is one of the tallest mountains in the Solar System, three times as tall as Mount Everest and more than twice the height of Mauna Kea the tallest mountain on Earth. Olympus Mons is the youngest of the large...

, the highest known mountain within the Solar System, and of Valles Marineris
Valles Marineris
Valles Marineris is a system of canyons that runs along the Martian surface east of the Tharsis region...

, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.

Until the first successful flyby of Mars occurred in 1965, by Mariner 4
Mariner 4
Mariner 4 was the fourth in a series of spacecraft, launched on November 28, 1964, intended for planetary exploration in a flyby mode and performed the first successful flyby of the planet Mars, returning the first pictures of the Martian surface...

, many speculated about the presence of liquid water on the planet's surface. This was based on observed periodic variations in light and dark patches, particularly in the polar latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s, which appeared to be seas and continents; long, dark striations
Striation (geology)
In geology, a striation means linear furrows generated from fault movement; The striation's direction reveal the movement directions in the fault plane. Similar striations can occur with glaciation....

 were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusion
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...

s, though geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface. In 2005, radar data revealed the presence of large quantities of water ice at the poles, and at mid-latitudes. The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007. The Phoenix
Phoenix (spacecraft)
Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...

lander directly sampled water ice in shallow Martian soil on July 31, 2008.

Mars has two moons, Phobos
Phobos (moon)
Phobos is the larger and closer of the two natural satellites of Mars. Both moons were discovered in 1877. With a mean radius of , Phobos is 7.24 times as massive as Deimos...

 and Deimos
Deimos (moon)
Deimos is the smaller and outer of Mars's two moons . It is named after Deimos, a figure representing dread in Greek Mythology. Its systematic designation is '.-Discovery:Deimos was discovered by Asaph Hall, Sr...

, which are small and irregularly shaped. These may be captured asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s, similar to 5261 Eureka
5261 Eureka
5261 Eureka is the first asteroid discovered that turned out to be a Mars trojan asteroid. It was discovered by David H. Levy and Henry Holt at Palomar Observatory on June 20, 1990. It trails Mars at a distance varying by only 0.3 AU during each revolution...

, a Martian trojan asteroid. Mars is currently host to three functional orbiting spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

: Mars Odyssey, Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...

, and the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

. On the surface are the Mars Exploration Rover
Mars Exploration Rover
NASA's Mars Exploration Rover Mission is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars...

 Opportunity
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...

and its recently decommissioned twin, Spirit
Spirit rover
Spirit, MER-A , is a robotic rover on Mars, active from 2004 to 2010. It was one of two rovers of NASA's ongoing Mars Exploration Rover Mission. It landed successfully on Mars at 04:35 Ground UTC on January 4, 2004, three weeks before its twin, Opportunity , landed on the other side of the planet...

, along with several other inert landers and rovers, both successful and unsuccessful. The Phoenix lander completed its mission on the surface in 2008. Observations by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

's now-defunct Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

show evidence that parts of the southern polar ice cap have been receding. Observations by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

's Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

 have revealed possible flowing water during the warmest months on Mars.

Mars can easily be seen from Earth with the naked eye. Its apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 reaches −3.0 a brightness surpassed only by Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

, Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

, the Moon, and the Sun. Optical ground based telescopes are typically limited to resolving features about 300 km (186 miles) across when Earth and Mars are closest, because of Earth's atmosphere.

Physical characteristics


Mars has approximately half the diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

 of Earth. It is less dense than Earth, having about 15% of Earth's volume and 11% of the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

. Its surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...

 is only slightly less than the total area of Earth's dry land. While Mars is larger and more massive than Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

, Mercury has a higher density. This results in the two planets having a nearly identical gravitational pull at the surface—that of Mars is stronger by less than 1%. Mars is also roughly intermediate in size, mass, and surface gravity
Surface gravity
The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in...

 between Earth and Earth's Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 (the Moon is about half the diameter of Mars, whereas Earth is twice; the Earth is about nine times more massive than Mars, and the Moon one-ninth as massive). The red-orange appearance of the Martian surface is caused by iron(III) oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

, more commonly known as hematite, or rust.

Geology


Based on orbital observations and the examination of the Martian meteorite collection, the surface of Mars appears to be composed primarily of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

. Some evidence suggests that a portion of the Martian surface is more silica-rich than typical basalt, and may be similar to andesitic rocks on Earth; these observations may also be explained by silica glass. Much of the surface is deeply covered by finely grained iron(III) oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

 dust.

Although Mars has no evidence of a current structured global magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

, observations show that parts of the planet's crust have been magnetized, and that alternating polarity reversals of its dipole field have occurred in the past. This paleomagnetism
Paleomagnetism
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of...

 of magnetically susceptible minerals has properties that are very similar to the alternating bands found on the ocean floors of Earth. One theory, published in 1999 and re-examined in October 2005 (with the help of the Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

), is that these bands demonstrate plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 on Mars four billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....

 years ago, before the planetary dynamo
Dynamo theory
In geophysics, dynamo theory proposes a mechanism by which a celestial body such as the Earth or a star generates a magnetic field. The theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time...

 ceased to function and caused the planet's magnetic field to fade away.

Current models of the planet's interior imply a core region about 1,480 km in radius, consisting primarily of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 with about 14–17% sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

. This iron sulfide
Iron(II) sulfide
Iron sulfide or ferrous sulfide is a chemical compound with the formula . In practice, iron sulfides are often non-stoichiometric. Powdered iron sulfide is pyrophoric Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound with the formula . In practice, iron sulfides are...

 core is partially fluid, and has twice the concentration of the lighter elements than exist at Earth's core. The core is surrounded by a silicate mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

 that formed many of the tectonic and volcanic features on the planet, but now appears to be inactive. The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km. Earth's crust, averaging 40 km, is only one third as thick as Mars’ crust, relative to the sizes of the two planets.

During the Solar System's formation
Formation and evolution of the Solar System
The formation and evolution of the Solar System is estimated to have begun 4.568 billion years ago with the gravitational collapse of a small part of a giant molecular cloud...

, Mars was created out of the protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...

 that orbited the Sun as the result of a stochastic process
Stochastic process
In probability theory, a stochastic process , or sometimes random process, is the counterpart to a deterministic process...

 of run-away accretion. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points such as chlorine, phosphorus and sulphur are much more common on Mars than Earth; these elements were probably removed from areas closer to the Sun by the young Sun's powerful solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

.

After the formation of the planets, all were subjected to the "Late Heavy Bombardment
Late Heavy Bombardment
The Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...

". About 60% of the surface of Mars shows an impact record from that era. Much of the rest of the surface of Mars is probably underlain by immense impact basins that date from this time—there is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 km by 8,500 km, or roughly four times larger than the Moon's South Pole-Aitken basin
South Pole-Aitken basin
The South Pole-Aitken basin is an impact crater on Earth's Moon. Roughly in diameter and deep, it is one of the largest known impact craters in the Solar System. It is the largest, oldest and deepest basin recognized on the Moon. This moon basin was named for two features on opposing sides; the...

, the largest impact basin yet discovered. This theory suggests that Mars was struck by a Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

-sized body about four billion years ago. The event, thought to be the cause of the Martian hemispheric dichotomy, created the smooth Borealis basin that covers 40% of the planet.

The geological history of Mars can be split into many periods, but the following are the three primary periods:
  • Noachian period (named after Noachis Terra
    Noachis Terra
    Noachis Terra is an extensive southern landmass of the planet Mars. It lies west of the giant Hellas impact basin, roughly between the latitudes −20° and −80° and longitudes 30° west and 30° east, centered on ....

    ): Formation of the oldest extant surfaces of Mars, 4.5 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis
    Tharsis
    The Tharsis region on Mars is a vast volcanic plateau centered near the equator in Mars’ western hemisphere. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as...

     bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the period.
  • Hesperian period (named after Hesperia Planum): 3.5 billion years ago to 2.9–3.3 billion years ago. The Hesperian period is marked by the formation of extensive lava plains.
  • Amazonian period (named after Amazonis Planitia
    Amazonis Planitia
    Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces to the west of Olympus Mons in the Valles Marineris region of the Memnonia quadrangle, centered at...

    ): 2.9–3.3 Gyr ago billion years ago to present. Amazonian regions have few meteorite impact
    Impact event
    An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...

     craters, but are otherwise quite varied. Olympus Mons
    Olympus Mons
    Olympus Mons is a large volcanic mountain on the planet Mars. At a height of almost , it is one of the tallest mountains in the Solar System, three times as tall as Mount Everest and more than twice the height of Mauna Kea the tallest mountain on Earth. Olympus Mons is the youngest of the large...

     formed during this period, along with lava flows elsewhere on Mars.


Some geological activity is still taking place on Mars. The Athabasca Valles
Athabasca Valles
Athabasca Valles is an outflow channel on Mars, cut into its surface by catastrophic flooding. It is one of the youngest known of these structures, probably forming only in the geologically recent past of Mars. The flood produced distinctive "teardrop" landforms similar to those found in the...

 is home to sheet-like lava flows up to about 200 Mya. Water flows in the grabens called the Cerberus Fossae
Cerberus Fossae
The Cerberus Fossae are a series of semi-parallel fissures on Mars formed by faults which pulled the crust apart in the Cerberus region . Ripples seen at the bottom of the fault are sand blown by the wind ....

 occurred less than 20 Mya, indicating equally recent volcanic intrusions. On February 19, 2008, images from the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

showed evidence of an avalanche from a 700 m high cliff.

Soil



The Phoenix
Phoenix (spacecraft)
Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...

lander returned data showing Martian soil to be slightly alkaline and containing elements such as magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

, sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

, potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 and chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

. These nutrients are found in gardens on Earth, and are necessary for growth of plants. Experiments performed by the Lander showed that the Martian soil has a basic
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...

 pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 of 8.3, and may contain traces of the salt perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...

.

Streaks are common across Mars and new ones appear frequently on steep slopes of craters, troughs, and valleys. The streaks are dark at first and get lighter with age. Sometimes the streaks start in a tiny area which then spreads out for hundreds of metres. They have also been seen to follow the edges of boulders and other obstacles in their path. The commonly accepted theories include that they are dark underlying layers of soil revealed after avalanches of bright dust or dust devils. Several explanations have been put forward, some of which involve water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 or even the growth of organisms.

Hydrology



Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters. A permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

 mantle stretches from the pole to latitudes of about 60°.

Large quantities of water ice
Evolution of water on Mars and Earth
The evolution of water on either planet needs be understood in the context of the other terrestrial planetary bodies and their current water status.- Water Inventory of Mars:...

 are thought to be trapped underneath the thick cryosphere
Cryosphere
The cryosphere is the term which collectively describes the portions of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground . Thus there is a wide overlap with the hydrosphere...

 of Mars. Radar data from Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...

and the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

show large quantities of water ice both at the poles (July 2005) and at mid-latitudes (November 2008). The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.

Landforms
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...

 visible on Mars strongly suggest that liquid water has at least at times existed on the planet's surface. Huge linear swathes of scoured ground, known as outflow channels
Outflow channels
Outflow channels is the term used to describe extremely long, wide swathes of scoured ground on Mars, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope...

, cut across the surface in around 25 places. These are thought to record erosion which occurred during the catastrophic release of water from subsurface aquifers, though some of these structures have also been hypothesised to result from the action of glaciers or lava. The youngest of these channels are thought to have formed as recently as only a few million years ago. Elsewhere, particularly on the oldest areas of the martian surface, finer-scale, dendritic networks of valleys
Valley networks (Mars)
Valley networks are branching networks of valleys on Mars that superficially resemble terrestrial river drainage basins. They are found mainly incised into the terrain of the martian southern highlands, and are typically - though not always - of Noachian age...

 are spread across significant proportions of the landscape. Features of these valleys and their distribution very strongly imply that they were carved by runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

 resulting from rain or snow fall in early Mars history. Subsurface water flow and groundwater sapping
Groundwater sapping
Groundwater sapping is the geomorphic process in which groundwater exits a bank or hillslope laterally as seeps and springs and erodes soil from the slope. This often causes the slope to be undermined and undergo mass wasting, hence the word sapping....

 may play important subsidiary roles in some networks, but precipitation was probably the root cause of the incision in almost all cases.

There are also thousands of features along crater and canyon walls that appear similar to terrestrial gullies. The gullies tend to be in the highlands of the southern hemisphere and to face the Equator; all are poleward of 30° latitude. A number of authors have suggested that their formation process demands the involvement of liquid water, probably from melting ice, although others have argued for formation mechanisms involving carbon dioxide frost or the movement of dry dust. No partially degraded gullies have formed by weathering and no superimposed impact craters have been observed, indicating that these are very young features, possibly even active today.

Other geological features, such as delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

s and alluvial fans preserved in craters, also argue very strongly for warmer, wetter conditions at some interval or intervals in earlier Mars history. Such conditions necessarily require the widespread presence of crater lakes across a large proportion of the surface, for which there is also independent mineralogical, sedimentological and geomorphological evidence. Some authors have even gone so far as to argue that at times in the martian past, much of the low northern plains of the planet were covered with a true ocean hundreds of meters deep, though this remains controversial.

Further evidence that liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 water once existed on the surface of Mars comes from the detection of specific minerals such as hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...

 and goethite
Goethite
Goethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...

, both of which sometimes form in the presence of water. Some of the evidence believed to indicate ancient water basins and flows has been negated by higher resolution studies by the Mars Reconnaissance Orbiter. In 2004, Opportunity detected the mineral jarosite
Jarosite
Jarosite is a basic hydrous sulfate of potassium and iron with a chemical formula of KFe3+362. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides...

. This forms only in the presence of acidic water, which demonstrates that water once existed on Mars.

Polar caps


Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 ice (dry ice
Dry ice
Dry ice, sometimes referred to as "Cardice" or as "card ice" , is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue...

). When the poles are again exposed to sunlight, the frozen CO2 sublimes
Sublimation (physics)
Sublimation is the process of transition of a substance from the solid phase to the gas phase without passing through an intermediate liquid phase...

, creating enormous winds that sweep off the poles as fast as 400 km/h. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus cloud
Cirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...

s. Clouds of water-ice were photographed by the Opportunity
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...

rover in 2004.

The polar caps at both poles consist primarily of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only, while the south cap has a permanent dry ice cover about eight metres thick. The northern polar cap has a diameter of about 1,000 kilometres during the northern Mars summer, and contains about 1.6 million cubic km of ice, which if spread evenly on the cap would be 2 km thick. (This compares to a volume of 2.85 million cubic km (km3) for the Greenland ice sheet
Greenland ice sheet
The Greenland ice sheet is a vast body of ice covering , roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost long in a north-south direction, and its greatest width is at a latitude of 77°N, near its...

.) The southern polar cap has a diameter of 350 km and a thickness of 3 km. The total volume of ice in the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 million cubic km. Both polar caps show spiral troughs, which recent analysis of SHARAD
SHARAD
SHARAD is a subsurface sounding radar embarked on the Mars Reconnaissance Orbiter probe. It complements the MARSIS instrument on Mars Express, providing lower penetration capabilities but much finer resolution .SHARAD is developed under the responsibility of the Italian Space Agency SHARAD (Mars...

 ice penetrating radar has shown are a result of katabatic wind
Katabatic wind
A katabatic wind, from the Greek word katabatikos meaning "going downhill", is the technical name for a drainage wind, a wind that carries high density air from a higher elevation down a slope under the force of gravity. Such winds are sometimes also called fall winds...

s that spiral due to the Coriolis Effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

.

The seasonal frosting of some areas near the southern ice cap results in the formation of transparent 1 metre thick slabs of dry ice above the ground. With the arrival of spring, sunlight warms the subsurface and pressure from subliming CO2 builds up under a slab, elevating and ultimately rupturing it. This leads to geyser-like eruptions of CO2 gas mixed with dark basaltic sand or dust. This process is rapid, observed happening in the space of a few days, weeks or months, a rate of change rather unusual in geology—especially for Mars. The gas rushing underneath a slab to the site of a geyser carves a spider-like pattern of radial channels under the ice.

Geography



Although better remembered for mapping the Moon, Johann Heinrich Mädler and Wilhelm Beer were the first "areographers". They began by establishing that most of Mars’ surface features were permanent, and more precisely determining the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. Rather than giving names to the various markings, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a."

Today, features on Mars are named from a variety of sources. Albedo features are named for classical mythology. Craters larger than 60 kilometres (37.3 mi) are named for deceased scientists and writers and others who have contributed to the study of Mars. Craters smaller that 60 km are named for towns and villages of the world with populations of less than 100,000. Large valleys are named for the word mars or star in various languages, small valleys are named for rivers.

Large albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 features retain many of the older names, but are often updated to reflect new knowledge of the nature of the features. For example, Nix Olympica (the snows of Olympus) has become Olympus Mons (Mount Olympus). The surface of Mars as seen from Earth is divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian 'continents' and given names like Arabia Terra
Arabia Terra
Arabia Terra is a large upland region in the north of Mars in that lies mostly in the Arabia quadrangle. It is densely cratered and heavily eroded. This battered topography indicates great age, and Arabia Terra is presumed to be one of the oldest terrains on the planet...

 (land of Arabia) or Amazonis Planitia
Amazonis Planitia
Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces to the west of Olympus Mons in the Valles Marineris region of the Memnonia quadrangle, centered at...

 (Amazonian plain). The dark features were thought to be seas, hence their names Mare Erythraeum
Mare Erythraeum
Mare Erythraeum is a very large dark dusky region of Mars that can be viewed by even a small telescope. The name comes from the Latin for the Erythraean Sea, because it was originally thought to be a large sea of liquid water. It was included in Percival Lowell's 1895 map of Mars.-External links:*...

, Mare Sirenum and Aurorae Sinus
Aurorae Sinus
Aurorae Sinus is a dark feature in the southern hemisphere of the planet Mars. Together with albedo features contributed by Aonius Sinus and Solis Lacus, it is part of a feature known as the "eye of Mars"....

. The largest dark feature seen from Earth is Syrtis Major Planum. The permanent northern polar ice cap is named Planum Boreum
Planum Boreum
Planum Boreum is the northern polar plain on Mars. It extends northward from roughly 80°N and is centered at . Surrounding the high polar plain is a flat and featureless lowland plain called Vastitas Borealis which extends for approximately 1500 kilometres southwards, dominating the northern...

, while the southern cap is called Planum Australe
Planum Australe
Planum Australe is the southern polar plain on Mars. It extends southward of roughly 75°S and is centered at . The geology of this region was to be explored by the failed NASA mission Mars Polar Lander, which lost contact on entry into the Martian atmosphere.-Ice cap:Planum Australe is partially...

.

Mars’ equator is defined by its rotation, but the location of its Prime Meridian
Prime Meridian
The Prime Meridian is the meridian at which the longitude is defined to be 0°.The Prime Meridian and its opposite the 180th meridian , which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.An international...

 was specified, as was Earth's (at Greenwich
Greenwich
Greenwich is a district of south London, England, located in the London Borough of Greenwich.Greenwich is best known for its maritime history and for giving its name to the Greenwich Meridian and Greenwich Mean Time...

), by choice of an arbitrary point; Mädler and Beer selected a line in 1830 for their first maps of Mars. After the spacecraft Mariner 9
Mariner 9
Mariner 9 was a NASA space orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 13 of the same year, becoming the first spacecraft to orbit...

 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0
Airy-0
Airy-0 is a crater on Mars whose location defines the position of the prime meridian of that planet. It is about across and lies within the larger crater Airy in the region Sinus Meridiani....

), located in the Sinus Meridiani
Sinus Meridiani
Sinus Meridiani is a feature name for an albedo feature on Mars stretching east-west just south of that planet's equator. It was named by the French astronomer Camille Flammarion in the late 1870s.-Observational History:...

 ("Middle Bay" or "Meridian Bay"), was chosen for the definition of 0.0° longitude to coincide with the original selection.

Since Mars has no oceans and hence no 'sea level', a zero-elevation surface also had to be selected as a reference level; this is also called the areoid of Mars, analogous to the terrestrial geoid
Geoid
The geoid is that equipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest , and extended through the continents . According to C.F...

. Zero altitude is defined by the height at which there is 610.5 Pa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...

 (6.105 mbar) of atmospheric pressure. This pressure corresponds to the triple point
Triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...

 of water, and is about 0.6% of the sea level surface pressure on Earth (0.006 atm). In practice, today this surface is defined directly from satellite gravity measurements.

Impact topography


The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. Research in 2008 has presented evidence regarding a theory proposed in 1980 postulating that, four billion years ago, the northern hemisphere of Mars was struck by an object one-tenth to two-thirds the size of the Moon. If validated, this would make the northern hemisphere of Mars the site of an impact crater 10,600 km long by 8,500 km wide, or roughly the area of Europe, Asia, and Australia combined, surpassing the South Pole-Aitken basin
South Pole-Aitken basin
The South Pole-Aitken basin is an impact crater on Earth's Moon. Roughly in diameter and deep, it is one of the largest known impact craters in the Solar System. It is the largest, oldest and deepest basin recognized on the Moon. This moon basin was named for two features on opposing sides; the...

 as the largest impact crater in the Solar System.

Mars is scarred by a number of impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

s: a total of 43,000 craters with a diameter of 5 km or greater have been found. The largest confirmed of these is the Hellas impact basin
Hellas Planitia
Hellas Planitia, also known as the Hellas Impact Basin, is a huge, roughly circular impact basin located in the southern hemisphere of the planet Mars. It is the second or third largest impact crater and the largest visible impact crater known in the Solar System...

, a light albedo feature
Albedo feature
An albedo feature is a large area on the surface of a planet which shows a contrast in brightness or darkness with adjacent areas....

 clearly visible from Earth. Due to the smaller mass of Mars, the probability of an object colliding with the planet is about half that of the Earth. Mars is located closer to the asteroid belt, so it has an increased chance of being struck by materials from that source. Mars is also more likely to be struck by short-period comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

s, i.e., those that lie within the orbit of Jupiter. In spite of this, there are far fewer craters on Mars compared with the Moon because the atmosphere of Mars provides protection against small meteors. Some craters have a morphology that suggests the ground became wet after the meteor impacted.

Tectonic sites


The shield volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...

, Olympus Mons
Olympus Mons
Olympus Mons is a large volcanic mountain on the planet Mars. At a height of almost , it is one of the tallest mountains in the Solar System, three times as tall as Mount Everest and more than twice the height of Mauna Kea the tallest mountain on Earth. Olympus Mons is the youngest of the large...

 (Mount Olympus), at 27 km is the highest known mountain in the Solar System. It is an extinct volcano in the vast upland region Tharsis
Tharsis
The Tharsis region on Mars is a vast volcanic plateau centered near the equator in Mars’ western hemisphere. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as...

, which contains several other large volcanoes. Olympus Mons is over three times the height of Mount Everest
Mount Everest
Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...

, which in comparison stands at just over 8.8 km.

The large canyon, Valles Marineris
Valles Marineris
Valles Marineris is a system of canyons that runs along the Martian surface east of the Tharsis region...

 (Latin for Mariner
Mariner program
The Mariner program was a program conducted by the American space agency NASA that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1963 to 1973...

 Valleys
, also known as Agathadaemon in the old canal maps), has a length of 4,000 km and a depth of up to 7 km. The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. By comparison, the Grand Canyon
Grand Canyon
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, the 15th national park in the United States...

 on Earth is only 446 km long and nearly 2 km deep. Valles Marineris was formed due to the swelling of the Tharsis area which caused the crust in the area of Valles Marineris to collapse. Another large canyon is Ma'adim Vallis
Ma'adim Vallis
Ma'adim Vallis is one of the largest outflow channels on Mars, about 700 km long and significantly larger than Earth's Grand Canyon. It is over 20 km wide and 2 km deep in some places. It runs from a region of southern lowlands thought to have once contained a large group of lakes ...

 (Ma'adim is Hebrew for Mars). It is 700 km long and again much bigger than the Grand Canyon with a width of 20 km and a depth of 2 km in some places. It is possible that Ma'adim Vallis was flooded with liquid water in the past.

Caves


Images from the Thermal Emission Imaging System
Thermal Emission Imaging System
The Thermal Emission Imaging System is a camera on board the 2001 Mars Odyssey orbiter. It images Mars in the visible and infrared parts of the electromagnetic spectrum in order to determine the thermal properties of the surface and to refine the distribution of minerals on the surface of Mars as...

 (THEMIS) aboard NASA's Mars Odyssey orbiter
2001 Mars Odyssey
2001 Mars Odyssey is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectrometers and electronic imagers to hunt for evidence of past or...

 have revealed seven possible cave
Cave
A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...

 entrances on the flanks of the Arsia Mons
Arsia Mons
Arsia Mons is the southernmost of three volcanos on the Tharsis bulge near the equator of the planet Mars. To its north is Pavonis Mons, and north of that is Ascraeus Mons. The tallest mountain in the solar system, Olympus Mons, is to its northwest...

 volcano. The caves, named after loved ones of their discoverers, are collectively known as the "seven sisters." Cave entrances measure from 100 m to 252 m wide and they are believed to be at least 73 m to 96 m deep. Because light does not reach the floor of most of the caves, it is likely that they extend much deeper than these lower estimates and widen below the surface. "Dena" is the only exception; its floor is visible and was measured to be 130 m deep. The interiors of these caverns may be protected from micrometeoroids, UV radiation, solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...

s and high energy particles that bombard the planet's surface.

Atmosphere



Mars lost its magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...

 4 billion years ago, so the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 interacts directly with the Martian ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...

, lowering the atmospheric density by stripping away atoms from the outer layer. Both Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

 and Mars Express have detected these ionised atmospheric particles trailing off into space behind Mars. Compared to Earth, the atmosphere of Mars is quite rarefied. Atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 on the surface ranges from a low of 30 Pa (0.03 kPa) on Olympus Mons
Olympus Mons
Olympus Mons is a large volcanic mountain on the planet Mars. At a height of almost , it is one of the tallest mountains in the Solar System, three times as tall as Mount Everest and more than twice the height of Mauna Kea the tallest mountain on Earth. Olympus Mons is the youngest of the large...

 to over 1155 Pa (1.2 kPa) in the Hellas Planitia
Hellas Planitia
Hellas Planitia, also known as the Hellas Impact Basin, is a huge, roughly circular impact basin located in the southern hemisphere of the planet Mars. It is the second or third largest impact crater and the largest visible impact crater known in the Solar System...

, with a mean pressure at the surface level of 600 Pa (0.6 kPa). The surface pressure of Mars at its thickest is equal to the pressure found 35 km above the Earth's surface. This is less than 1% of the Earth's surface pressure (101.3 kPa). The scale height
Scale height
In various scientific contexts, a scale height is a distance over which a quantity decreases by a factor of e...

 of the atmosphere is about 10.8 km, which is higher than Earth's (6 km) because the surface gravity of Mars is only about 38% of Earth's, an effect offset by both the lower temperature and 50% higher average molecular weight of the atmosphere of Mars.

The atmosphere on Mars consists of 95% carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, 3% nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, 1.6% argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 and contains traces of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and water. The atmosphere is quite dusty, containing particulates about 1.5 µm in diameter which give the Martian sky a tawny
Tawny (color)
Tawny is a yellowish brown color. The word means "tan-colored," from Anglo-Norman tauné "associated with the brownish-yellow of tanned leather," from Old French tané "to tan hides," from Medieval Latin tannare, from tannum "crushed oak bark," used in tanning leather, probably from a Celtic source...

 color when seen from the surface.


Methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 has been detected in the Martian atmosphere with a mole fraction of about 30 ppb
PPB
PPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...

; it occurs in extended plumes, and the profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained 19,000 metric tons of methane, with an estimated source strength of 0.6 kilogram per second. The profiles suggest that there may be two local source regions, the first centered near 30° N, 260° W and the second near 0°, 310° W. It is estimated that Mars must produce 270 ton/year of methane.

The implied methane destruction lifetime may be as long as about 4 Earth years and as short as about 0.6 Earth years. This rapid turnover would indicate an active source of the gas on the planet. Volcanic
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....

 activity, comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

ary impacts, and the presence of methanogen
Methanogen
Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are classified as archaea, a group quite distinct from bacteria...

ic microbial
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

 life forms are among possible sources. Methane could also be produced by a non-biological process called serpentinization
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...

involving water, carbon dioxide, and the mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

, which is known to be common on Mars.

Climate




Of all the planets in the Solar System, the seasons of Mars are the most Earth-like, due to the similar tilts of the two planets' rotational axes. The lengths of the Martian seasons are about twice those of Earth's, as Mars’ greater distance from the Sun leads to the Martian year being about two Earth years long. Martian surface temperatures vary from lows of about -87 °C during the polar winters to highs of up to -5 °C in summers. The wide range in temperatures is due to the thin atmosphere which cannot store much solar heat, the low atmospheric pressure, and the low thermal inertia
Volumetric heat capacity
Volumetric heat capacity , also termed volume-specific heat capacity, describes the ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase change...

 of Martian soil. The planet is also 1.52 times as far from the sun as Earth, resulting in just 43% of the amount of sunlight.

If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...

 is similar to Earth's. The comparatively large eccentricity of the Martian orbit has a significant effect. Mars is near perihelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...

 when it is summer in the southern hemisphere and winter in the north, and near aphelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...

 when it is winter in the southern hemisphere and summer in the north. As a result, the seasons in the southern hemisphere are more extreme and the seasons in the northern are milder than would otherwise be the case. The summer temperatures in the south can reach up to 30 °C (86 °F) warmer than the equivalent summer temperatures in the north.

Mars also has the largest dust storm
Dust storm
A dust / sand storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, causing soil to move from one place and deposition...

s in our Solar System. These can vary from a storm over a small area, to gigantic storms that cover the entire planet. They tend to occur when Mars is closest to the Sun, and have been shown to increase the global temperature.

Orbit and rotation



Mars’ average distance from the Sun is roughly 230 million km (1.5 AU) and its orbital period is 687 (Earth) days. The solar day (or sol
Timekeeping on Mars
Various schemes have been used or proposed to keep track of time and date on the planet Mars independently of Earth time and calendars.Mars has an axial tilt and a rotation period similar to those of Earth. Thus it experiences seasons of spring, summer, autumn and winter much like Earth, and its...

) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours.

The axial tilt of Mars is 25.19 degrees, which is similar to the axial tilt of the Earth. As a result, Mars has seasons like the Earth, though on Mars they are nearly twice as long given its longer year. Currently the orientation of the north pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

 of Mars is close to the star Deneb
Deneb
Deneb is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars...

. Mars passed its perihelion in April 2009 and its aphelion in March 2010. The next perihelion comes in March 2011 and the next aphelion in February 2012.

Mars has a relatively pronounced orbital eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...

 of about 0.09; of the seven other planets in the Solar System, only Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

 shows greater eccentricity. It is known that in the past Mars has had a much more circular orbit than it does currently. At one point 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today. The Mars cycle of eccentricity is 96,000 Earth years compared to the Earth's cycle of 100,000 years. Mars also has a much longer cycle of eccentricity with a period of 2.2 million Earth years, and this overshadows the 96,000-year cycle in the eccentricity graphs. For the last 35,000 years the orbit of Mars has been getting slightly more eccentric because of the gravitational effects of the other planets. The closest distance between the Earth and Mars will continue to mildly decrease for the next 25,000 years.

The image to the left shows a comparison between Mars and Ceres
1 Ceres
Ceres, formally 1 Ceres, is the smallest identified dwarf planet in the Solar System and the only one in the asteroid belt. With a diameter of about 950 km, Ceres is by far the largest and most-massive asteroid, comprising about a third of the mass of the asteroid belt. Discovered on 1 January 1801...

, a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

 in the Asteroid Belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...

, as seen from the north ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...

 pole, while the image to the right is as seen from the ascending node. The segments of orbits south of the ecliptic are plotted in darker colors. The perihelia (q) and aphelia (Q) are labelled with the date of the nearest passage. The orbit of Mars is shown in red, Ceres is in yellow.


Moons


Mars has two relatively small natural moons, Phobos
Phobos (moon)
Phobos is the larger and closer of the two natural satellites of Mars. Both moons were discovered in 1877. With a mean radius of , Phobos is 7.24 times as massive as Deimos...

 and Deimos
Deimos (moon)
Deimos is the smaller and outer of Mars's two moons . It is named after Deimos, a figure representing dread in Greek Mythology. Its systematic designation is '.-Discovery:Deimos was discovered by Asaph Hall, Sr...

, which orbit close to the planet. Asteroid capture is a long-favored theory but their origin remains uncertain. Both satellites were discovered in 1877 by Asaph Hall
Asaph Hall
Asaph Hall III was an American astronomer who is most famous for having discovered the moons of Mars in 1877...

, and are named after the characters Phobos
Phobos (mythology)
Phobos is the personification of horror in Greek mythology. He is the offspring of Ares and Aphrodite. He was known for accompanying Ares into battle along with his brother, Deimos, the goddess Enyo, and his father’s attendants. Timor is his Roman equivalent...

 (panic/fear) and Deimos
Deimos (mythology)
In Greek mythology, Deimos was the personification of terror.He was the son of Ares and Aphrodite. He is the twin brother of Phobos and the goddess Enyo who accompanied Ares into battle, as well as his father's attendants, Trembling, Fear, Dread, and Panic...

 (terror/dread) who, in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

, accompanied their father Ares
Ares
Ares is the Greek god of war. He is one of the Twelve Olympians, and the son of Zeus and Hera. In Greek literature, he often represents the physical or violent aspect of war, in contrast to the armored Athena, whose functions as a goddess of intelligence include military strategy and...

, god of war, into battle. Ares was known as Mars to the Romans.

From the surface of Mars, the motions of Phobos and Deimos appear very different from that of our own moon. Phobos rises in the west, sets in the east, and rises again in just 11 hours. Deimos, being only just outside synchronous orbit
Synchronous orbit
A synchronous orbit is an orbit in which an orbiting body has a period equal to the average rotational period of the body being orbited , and in the same direction of rotation as that body.-Properties:...

—where the orbital period would match the planet's period of rotation—rises as expected in the east but very slowly. Despite the 30 hour orbit of Deimos, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, then just as long again to rise.

Because the orbit of Phobos is below synchronous altitude, the tidal force
Tidal force
The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force per unit mass exerted on one body by a second body is not constant across its diameter, the side nearest to the second being more attracted by it than the side...

s from the planet Mars are gradually lowering its orbit. In about 50 million years it will either crash into Mars’ surface or break up into a ring structure around the planet.

The origin of the two moons is not well understood. Their low albedo and carbonaceous chondrite
Carbonaceous chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...

 composition have been regarded as similar to asteroids, supporting the capture theory. The unstable orbit of Phobos would seem to point towards a relatively recent capture. But both have circular orbit
Circular orbit
A circular orbit is the orbit at a fixed distance around any point by an object rotating around a fixed axis.Below we consider a circular orbit in astrodynamics or celestial mechanics under standard assumptions...

s, very near the equator, which is very unusual for captured objects and the required capture dynamics are complex. Accretion early in the history of Mars is also plausible but would not account for a composition resembling asteroids rather than Mars itself, if that is confirmed.

A third possibility is the involvement of a third body or some kind of impact disruption. More recent lines of evidence for Phobos having a highly porous interior and suggesting a composition containing mainly phyllosilicates and other minerals known from Mars, point toward an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the prevailing theory
Giant impact hypothesis
The giant impact hypothesis states that the Moon was created out of the debris left over from a collision between the young Earth and a Mars-sized body. The colliding body is sometimes called Theia for the mythical Greek Titan who was the mother of Selene, the goddess of the moon.The giant impact...

 for the origin of Earth's moon. While the VNIR
VNIR
VNIR is an initialism for visible and near-infrared, a portion of the electromagnetic spectrum having wavelengths between approximately 400 and 1400 nanometers ...

 spectra of the moons of Mars resemble those of outer belt asteroids, the thermal infrared spectra of Phobos are reported to be inconsistent with chondrite
Chondrite
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...

s of any class.

Search for life


The current understanding of planetary habitability
Planetary habitability
Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...

—the ability of a world to develop and sustain life—favors planets that have liquid water on their surface. This most often requires that the orbit of a planet lie within the habitable zone, which for the Sun currently extends from just beyond Venus to about the semi-major axis
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...

 of Mars. During perihelion Mars dips inside this region, but the planet's thin (low-pressure) atmosphere prevents liquid water from existing over large regions for extended periods. The past flow of liquid water demonstrates the planet's potential for habitability. Some recent evidence has suggested that any water on the Martian surface may have been too salty and acidic to support regular terrestrial life.

The lack of a magnetosphere and extremely thin atmosphere of Mars are a challenge: the planet has little heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 across its surface, poor insulation against bombardment of the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 and insufficient atmospheric pressure to retain water in a liquid form (water instead sublimates to a gaseous state). Mars is also nearly, or perhaps totally, geologically dead; the end of volcanic activity has apparently stopped the recycling of chemicals and minerals between the surface and interior of the planet.

Evidence suggests that the planet was once significantly more habitable than it is today, but whether living organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s ever existed there remains unknown. The Viking probes of the mid-1970s carried experiments designed to detect microorganisms in Martian soil at their respective landing sites and had positive results, including a temporary increase of CO2 production on exposure to water and nutrients. This sign of life was later disputed by some scientists, resulting in a continuing debate, with NASA scientist Gilbert Levin
Gilbert Levin
Gilbert Levin is an American engineer, the founder of Spherix and famous for experiments on Mars soil by the Viking program and the development of tagatose.Levin is a member of the "International Committee Against Mars Sample Return" ....

 asserting that Viking may have found life. A re-analysis of the Viking data, in light of modern knowledge of extremophile
Extremophile
An extremophile is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth. In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles...

 forms of life, has suggested that the Viking tests were not sophisticated enough to detect these forms of life. The tests could even have killed a (hypothetical) life form. Tests conducted by the Phoenix Mars lander have shown that the soil has a very alkaline pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 and it contains magnesium, sodium, potassium and chloride. The soil nutrients may be able to support life but life would still have to be shielded from the intense ultraviolet light.

At the Johnson space center lab, some fascinating shapes have been found in the meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

 ALH84001
ALH84001
Allan Hills 84001 is a meteorite that was found in Allan Hills, Antarctica on December 27, 1984 by a team of U.S. meteorite hunters from the ANSMET project. Like other members of the group of SNCs , ALH 84001 is thought to be from Mars. However, it does not fit into any of the previously...

, which is thought to have originated from Mars. Some scientists propose that these geometric shapes could be fossilized microbes extant on Mars before the meteorite was blasted into space by a meteor strike and sent on a 15 million-year voyage to Earth. An exclusively inorganic origin for the shapes has also been proposed.

Small quantities of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

 recently detected by Mars orbiters are both claimed to be hints for life, as these chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s would quickly break down in the Martian atmosphere. It is remotely possible that these compounds may instead be replenished by volcanic or geological means such as serpentinization.

Exploration



Dozens of spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

, including orbiter
Orbiter
An orbiter is a space probe that orbits a planet.-Asteroids:*NEAR Shoemaker...

s, landers
Lander (spacecraft)
A lander is a spacecraft which descends toward and comes to rest on the surface of an astronomical body. For bodies with atmospheres, the landing is called atmospheric reentry and the lander descends as a re-entry vehicle...

, and rovers
Rover (space exploration)
A rover is a space exploration vehicle designed to move across the surface of a planet or other astronomical body. Some rovers have been designed to transport members of a human spaceflight crew; others have been partially or fully autonomous robots...

, have been sent to Mars by the Soviet Union
Soviet space program
The Soviet space program is the rocketry and space exploration programs conducted by the former Union of Soviet Socialist Republics from the 1930s until its dissolution in 1991...

, the United States
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

, Europe, and Japan to study the planet's surface, climate, and geology. As of 2008, the price of transporting material from the surface of Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 to the surface of Mars is approximately US$309,000 per kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

.

Active probes at the Martian system as of 2011 include the Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

 (since 2006), Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...

 (since 2003), 2001 Mars Odyssey
2001 Mars Odyssey
2001 Mars Odyssey is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectrometers and electronic imagers to hunt for evidence of past or...

 (since 2001), and on the surface, Opportunity Rover
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...

 (since 2004). More recently concluded missions include Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

 (1997–2006) and Spirit Rover
Spirit rover
Spirit, MER-A , is a robotic rover on Mars, active from 2004 to 2010. It was one of two rovers of NASA's ongoing Mars Exploration Rover Mission. It landed successfully on Mars at 04:35 Ground UTC on January 4, 2004, three weeks before its twin, Opportunity , landed on the other side of the planet...

 (2004–2010). Recently launched missions include, Mars Science Laboratory
Mars Science Laboratory
The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...

 (aka Curiosity), and Phobos-Grunt
Phobos-Grunt
Fobos-Grunt or Phobos-Grunt was an attempted Russian sample return mission to Phobos, one of the moons of Mars. It was launched on 9 November 2011 at 02:16 local time from the Baikonur Cosmodrome, but subsequent rocket burns intended to set the craft on a course for Mars failed, leaving it...

, both in 2011.

Roughly two-thirds of all spacecraft destined for Mars have failed in one manner or another before completing or even beginning their missions, including the difficult late 20th century period of early pioneers and first-timers. Mission failures are typically ascribed to technical problems, and missions planners have to balance technology and mission goals. Some of the latest failures include Beagle 2
Beagle 2
Beagle 2 was an unsuccessful British landing spacecraft that formed part of the European Space Agency's 2003 Mars Express mission. All contact with it was lost upon its separation from the Mars Express six days before its scheduled entry into the atmosphere...

 (2003), Mars Climate Orbiter
Mars Climate Orbiter
The Mars Climate Orbiter was a 338 kilogram robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander...

 (1999), and Mars 96
Mars 96
Mars 96 was a failed Mars mission launched in 1996 to investigate Mars by the Russian Space Forces and not directly related to the Soviet Mars probe program of the same name. After failure of the second fourth-stage burn, the probe assembly re-entered the Earth's atmosphere, breaking up over a...

 (1996).

Past missions


The first successful fly-by of Mars was on July 14–15, 1965, by NASA's Mariner 4
Mariner 4
Mariner 4 was the fourth in a series of spacecraft, launched on November 28, 1964, intended for planetary exploration in a flyby mode and performed the first successful flyby of the planet Mars, returning the first pictures of the Martian surface...

. On November 14, 1971 Mariner 9
Mariner 9
Mariner 9 was a NASA space orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 13 of the same year, becoming the first spacecraft to orbit...

 became the first space probe to orbit another planet when it entered into orbit around Mars. The first objects to successfully land on the surface were two Soviet probes: Mars 2
Mars 2
The Mars program was a series of Mars unmanned landers and orbiters launched by the Soviet Union in the early 1970s.The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with an orbiter and an attached lander; they were the first human artifacts to impact the surface of Mars...

 on November 27 and Mars 3
Mars 3
The Mars 3 was an unmanned space probe of the Mars program, a series of unmanned Mars landers and orbiters launched by the Soviet Union in the early 1970s....

 on December 2, 1971, but both ceased communicating within seconds of landing. The 1975 NASA launches of the Viking program
Viking program
The Viking program consisted of a pair of American space probes sent to Mars, Viking 1 and Viking 2. Each spacecraft was composed of two main parts, an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface...

 consisted of two orbiters, each having a lander; both landers successfully touched down in 1976. Viking 1
Viking 1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and until May 19, 2010 held the record for the second longest Mars surface mission of 6 years and 116 days .- Mission :Following...

 remained operational for six years, Viking 2
Viking 2
The Viking 2 mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the Viking 1 mission. The Viking 2 lander operated on the surface for 1,281 Mars days and was turned off on 11 April 1980 when its batteries failed...

 for three. The Viking landers relayed color panoramas of Mars and the orbiters mapped the surface so well that the images remain in use.

The Soviet probes Phobos 1 and 2
Phobos program
The Phobos program was an unmanned space mission consisting of two probes launched by the Soviet Union to study Mars and its moons Phobos and Deimos. Phobos 2 became a Mars orbiter and returned 38 images with a resolution of up to 40 meters...

 were sent to Mars in 1988 to study Mars and its two moons. Phobos 1 lost contact on the way to Mars. Phobos 2, while successfully photographing Mars and Phobos, failed just before it was set to release two landers to the surface of Phobos.

Following the 1992 failure of the Mars Observer
Mars Observer
The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...

 orbiter, the NASA Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

 achieved Mars orbit in 1997. This mission was a complete success, having finished its primary mapping mission in early 2001. Contact was lost with the probe in November 2006 during its third extended program, spending exactly 10 operational years in space. The NASA Mars Pathfinder
Mars Pathfinder
Mars Pathfinder was an American spacecraft that landed a base station with roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight wheeled robotic rover named Sojourner.Launched on December 4, 1996 by NASA aboard a Delta II booster a...

, carrying a robotic exploration vehicle Sojourner, landed in the Ares Vallis
Ares Vallis
Ares Vallis is an outflow channel on Mars, named after the Greek name for Mars: Ares, the god of war; it appears to have been carved by fluids, perhaps water...

 on Mars in the summer of 1997, returning many images.
The NASA Phoenix
Phoenix (spacecraft)
Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...

 Mars lander arrived on the north polar region of Mars on May 25, 2008. Its robotic arm was used to dig into the Martian soil and the presence of water ice was confirmed on June 20. The mission concluded on November 10, 2008 after contact was lost.

The Dawn
Dawn Mission
Dawn is a NASA spacecraft tasked with the exploration and study of the two largest members of the asteroid belt – Vesta and the dwarf planet Ceres. The spacecraft was constructed with some European cooperation, with partners in Germany, Italy, and the Netherlands providing Dawns framing...

 spacecraft flew by Mars in February 2009 for a gravity assist on its way to investigate Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....

 and then Ceres.

Spirit Rover
Spirit rover
Spirit, MER-A , is a robotic rover on Mars, active from 2004 to 2010. It was one of two rovers of NASA's ongoing Mars Exploration Rover Mission. It landed successfully on Mars at 04:35 Ground UTC on January 4, 2004, three weeks before its twin, Opportunity , landed on the other side of the planet...

 (MER-A) was active from 2004 until 2010, when it stopped sending data.

Current missions


The NASA Mars Odyssey orbiter entered Mars orbit in 2001. Odyssey's Gamma Ray Spectrometer
Gamma Ray Spectrometer
Gamma Ray Spectrometer is a gamma-ray spectrometer on the 2001 Mars Odyssey spacecraft, a space probe orbiting the planet Mars since 2001. Part of the United State's NASA's Mars Surveyor Program, it returns geological data about Mars' surface such as identifying elements and the location of water...

 detected significant amounts of hydrogen in the upper metre or so of regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...

 on Mars. This hydrogen is thought to be contained in large deposits of water ice.

The Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...

 mission of the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

 (ESA) reached Mars in 2003. It carried the Beagle 2
Beagle 2
Beagle 2 was an unsuccessful British landing spacecraft that formed part of the European Space Agency's 2003 Mars Express mission. All contact with it was lost upon its separation from the Mars Express six days before its scheduled entry into the atmosphere...

 lander, which failed during descent and was declared lost in February, 2004. In early 2004 the Planetary Fourier Spectrometer
Planetary Fourier Spectrometer
The Planetary Fourier Spectrometer is an infrared spectrometer built by the Istituto Nazionale di Astrofisica along with the Istituto di Fisica dello spazio Interplanetario and the Consiglio Nazionale delle Ricerche...

 team announced the orbiter had detected methane in the Martian atmosphere. ESA announced in June 2006 the discovery of aurorae
Aurora (astronomy)
An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...

 on Mars.

In January 2004, the NASA twin Mars Exploration Rovers named Spirit
Spirit rover
Spirit, MER-A , is a robotic rover on Mars, active from 2004 to 2010. It was one of two rovers of NASA's ongoing Mars Exploration Rover Mission. It landed successfully on Mars at 04:35 Ground UTC on January 4, 2004, three weeks before its twin, Opportunity , landed on the other side of the planet...

(MER-A) and Opportunity
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...

(MER-B) landed on the surface of Mars. Both have met or exceeded all their targets. Among the most significant scientific returns has been conclusive evidence that liquid water existed at some time in the past at both landing sites. Martian dust devils and windstorms have occasionally cleaned both rovers' solar panels, and thus increased their lifespan.

On March 10, 2006, the NASA Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

 (MRO) probe arrived in orbit to conduct a two-year science survey. The orbiter will map the Martian terrain and weather to find suitable landing sites for upcoming lander missions. The MRO snapped the first image of a series of active avalanche
Avalanche
An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...

s near the planet's north pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

, scientists said March 3, 2008.

En route


The joint Russian and Chinese Phobos-Grunt
Phobos-Grunt
Fobos-Grunt or Phobos-Grunt was an attempted Russian sample return mission to Phobos, one of the moons of Mars. It was launched on 9 November 2011 at 02:16 local time from the Baikonur Cosmodrome, but subsequent rocket burns intended to set the craft on a course for Mars failed, leaving it...

 mission to return samples of the Martian moon, Phobos, launched in 2011, but the failure of the probe to fire its engine has severely complicated the mission. The Russian Federal Space Agency is currently in contact with the probe and attempting to remedy the error(s).

The Mars Science Laboratory
Mars Science Laboratory
The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...

, named Curiosity, launched on 26 November, 2011, and plans reach Mars in August 2012. It is larger and more advanced than the Mars Exploration Rovers, with a movement rate of 90 m/h
Metre per hour
Metre per hour is a metric unit of both speed and velocity . Its symbol is m/h or m·h−1 Metre per hour (American spelling: meter per hour) is a metric unit of both speed (scalar) and velocity (Vector (geometry)). Its symbol is m/h or m·h−1 Metre per hour (American spelling: meter per...

. Experiments include a laser chemical sampler that can deduce the make-up of rocks at a distance of 13 m.

Future missions


In 2008, NASA announced MAVEN
Maven
A maven is a trusted expert in a particular field, who seeks to pass knowledge on to others. The word maven comes from Hebrew, via Yiddish, and means one who understands, based on an accumulation of knowledge.-History:...

, a robotic mission in 2013 to provide information about the atmosphere of Mars. In 2018 the ESA plans to launch its first Rover to Mars; the ExoMars
ExoMars
ExoMars is a European-led robotic mission to Mars currently under development by the European Space Agency with collaboration by NASA...

 rover will be capable of drilling 2 m into the soil in search of organic molecules.

The Finnish-Russian MetNet
MetNet
MetNet is an atmospheric science mission to Mars, initiated and defined by the Finnish Meteorological Institute. The mission includes sending several tens of MetNet landers on the Martian surface. The objective is to establish a widespread surface observation network on Mars to investigate the...

, is mission concept where multiple small vehicles on Mars to establish a widespread observation network to investigate the planet's atmospheric structure, physics and meteorology. MetNet was considered for a piggyback launch on the Russian Phobos-Grunt mission, but not selected.

Manned mission goals



The ESA hopes to land humans on Mars between 2030 and 2035. This will be preceded by successively larger probes, starting with the launch of the ExoMars probe and a joint NASA-ESA Mars sample return mission
Mars Sample Return Mission
A Mars sample return mission would be a spaceflight mission to collect rock and dust samples from Mars and to return them to Earth for analysis...

.

Manned exploration by the United States was identified as a long-term goal in the Vision for Space Exploration
Vision for Space Exploration
The Vision for Space Exploration is the United States space policy which was announced on January 14, 2004 by President George W. Bush. It is seen as a response to the Space Shuttle Columbia disaster, the state of human spaceflight at NASA, and a way to regain public enthusiasm for space...

 announced in 2004 by then US President George W. Bush
George W. Bush
George Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....

. The planned Orion
Orion (spacecraft)
Orion is a spacecraft designed by Lockheed Martin for NASA, the space agency of the United States. Orion development began in 2005 as part of the Constellation program, where Orion would fulfill the function of a Crew Exploration Vehicle....

spacecraft would be used to send a human expedition to Earth's moon by 2020 as a stepping stone to a Mars expedition. On September 28, 2007, NASA administrator Michael D. Griffin
Michael D. Griffin
Michael Douglas Griffin is an American physicist and aerospace engineer. From April 13, 2005 to January 20, 2009 he served as Administrator of NASA, the space agency of the United States...

 stated that NASA aims to put a man on Mars by 2037.

Mars Direct
Mars Direct
Mars Direct is a proposal for a manned mission to Mars. Proponents of the scheme have claimed it to be both cost-effective and that it can be conducted with current technology. It was originally detailed in a research paper by NASA engineers Robert Zubrin and David Baker in 1990, and later expanded...

, a low-cost human mission proposed by Robert Zubrin
Robert Zubrin
Robert Zubrin is an American aerospace engineer and author, best known for his advocacy of the manned exploration of Mars. He was the driving force behind Mars Direct—a proposal intended to produce significant reductions in the cost and complexity of such a mission...

, founder of the Mars Society
Mars Society
The Mars Society is an international space advocacy non-profit organization dedicated to promoting the human exploration and settlement of the planet Mars. It was founded by Robert Zubrin and others in 1998 and attracted the support of notable science fiction writers and filmmakers, including Kim...

, would use heavy-lift Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...

 class rockets, such as the Space X Falcon X, or, the Ares V
Ares V
The Ares V was the planned cargo launch component of the Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also planned to carry supplies for a human presence on Mars...

, to skip orbital construction, LEO rendezvous, and lunar fuel depots. A modified proposal, called "Mars to Stay
Mars to Stay
Mars to Stay missions propose astronauts sent to Mars for the first time should stay there indefinitely, both to reduce cost and to ensure permanent settlement of Mars. Among many notable Mars to Stay advocates, former Apollo astronaut Buzz Aldrin has been particularly outspoken, suggesting in...

", involves not returning the first immigrant explorers immediately, if ever (see Colonization of Mars
Colonization of Mars
The colonization of Mars by humans is the focus of speculation and serious study because the surface conditions and availability of water on Mars make it arguably the most hospitable planet in the solar system other than Earth...

).

Astronomy on Mars




With the existence of various orbiters, landers, and rovers, it is now possible to study astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 from the Martian skies. While Mars’ moon Phobos appears about one third the angular diameter
Angular diameter
The angular diameter or apparent size of an object as seen from a given position is the “visual diameter” of the object measured as an angle. In the vision sciences it is called the visual angle. The visual diameter is the diameter of the perspective projection of the object on a plane through its...

 of the full Moon as it appears from Earth, Deimos appears more or less star-like, and appears only slightly brighter than Venus does from Earth.

There are also various phenomena well-known on Earth that have now been observed on Mars, such as meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

s and auroras. A transit of the Earth as seen from Mars
Transit of Earth from Mars
A transit of Earth across the Sun as seen from Mars takes place when the planet Earth passes directly between the Sun and Mars, obscuring a small part of the Sun's disc for an observer on Mars. During a transit, Earth can be seen from Mars as a small black disc moving across the face of the Sun...

 will occur on November 10, 2084. There are also transits of Mercury
Transit of Mercury from Mars
A transit of Mercury across the Sun as seen from Mars takes place when the planet Mercury passes directly between the Sun and Mars, obscuring a small part of the Sun's disc for an observer on Mars...

 and transits of Venus
Transit of Venus from Mars
A transit of Venus across the Sun as seen from Mars takes place when the planet Venus passes directly between the Sun and Mars, obscuring a small part of the Sun's disc for an observer on Mars...

, and the moons Phobos and Deimos are of sufficiently small angular diameter
Angular diameter
The angular diameter or apparent size of an object as seen from a given position is the “visual diameter” of the object measured as an angle. In the vision sciences it is called the visual angle. The visual diameter is the diameter of the perspective projection of the object on a plane through its...

 that their partial "eclipses" of the Sun are best considered transits (see Transit of Deimos from Mars
Transit of Deimos from Mars
A transit of Deimos across the Sun as seen from Mars takes place when Deimos passes directly between the Sun and a point on the surface of Mars, obscuring a small part of the Sun's disc for an observer on Mars...

).

Viewing


Because the orbit of Mars is eccentric its apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 at opposition from the Sun can range from −3.0 to −1.4. The minimum brightness is magnitude +1.6 when the planet is in conjunction with the Sun. Mars usually appears a distinct yellow, orange, or reddish color; the actual color of Mars is closer to butterscotch
Butterscotch
Butterscotch is a type of confectionery whose primary ingredients are brown sugar and butter, although other ingredients such as corn syrup, cream, vanilla, and salt are part of some recipes...

, and the redness seen is just dust in the planet's atmosphere; considering this NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

's Spirit rover has taken pictures of a greenish-brown, mud-colored landscape with blue-grey rocks and patches of light red colored sand. When farthest away from the Earth, it is more than seven times as far from the latter as when it is closest. When least favorably positioned, it can be lost in the Sun's glare for months at a time. At its most favorable times—at 15- or 17-year intervals, and always between late July and late September—Mars shows a wealth of surface detail to a telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

. Especially noticeable, even at low magnification, are the polar ice cap
Polar ice cap
A polar ice cap is a high latitude region of a planet or natural satellite that is covered in ice. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of...

s.

As Mars approaches opposition it begins a period of retrograde motion, which means it will appear to move backwards in a looping motion with respect to the background stars. The duration of this retrograde motion lasts for about 72 days, and Mars reaches its peak luminosity in the middle of this motion.

Relative


The point Mars’ geocentric longitude is 180° different from the Sun's is known as opposition, which is near the time of closest approach to the Earth. The time of opposition can occur as much as 8½ days away from the closest approach. The distance at close approach varies between about 54 and about 103 million km due to the planets' elliptical
Ellipse
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...

 orbits, which causes comparable variation in angular size. The last Mars opposition occurred on January 29, 2010. The next one will occur on March 3, 2012 at a distance of about 100 million km. The average time between the successive oppositions of Mars, its synodic period, is 780 days but the number of days between the dates of successive oppositions can range from 764 to 812.

As Mars approaches opposition it begins a period of retrograde motion, which makes it appear to move backwards in a looping motion relative to the background stars. The duration of this retrograde motion is about 72 days.

Absolute, around the present time


Mars made its closest approach to Earth and maximum apparent brightness in nearly 60,000 years, 55,758,006 km , magnitude
Magnitude (astronomy)
Magnitude is the logarithmic measure of the brightness of an object, in astronomy, measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths.-Background:...

 −2.88, on 27 August 2003 at 9:51:13 UT. This occurred when Mars was one day from opposition and about three days from its perihelion, making Mars particularly easy to see from Earth. The last time it came so close is estimated to have been on September 12, 57 617 BC
Middle Paleolithic
The Middle Paleolithic is the second subdivision of the Paleolithic or Old Stone Age as it is understood in Europe, Africa and Asia. The term Middle Stone Age is used as an equivalent or a synonym for the Middle Paleolithic in African archeology. The Middle Paleolithic and the Middle Stone Age...

, the next time being in 2287. This record approach was only very slightly closer than other recent close approaches. For instance, the minimum distance on August 22, 1924 was , and the minimum distance on August 24, 2208 will be .

An email sent during the close approach in 2003 has, in succeeding years, repeatedly spawned hoax emails
Mars hoax
The Mars hoax was an e-mail-circulated hoax that originated in 2003, claiming that Mars will look as large as the full Moon to the naked eye on August 27, 2003...

 saying that Mars will make its closest approach for thousands of years, and will look as big as the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

.

Historical observations


The history of observations of Mars is marked by the oppositions of Mars, when the planet is closest to Earth and hence is most easily visible, which occur every couple of years. Even more notable are the perihelic oppositions of Mars which occur every 15 or 17 years, and are distinguished because Mars is close to perihelion, making it even closer to Earth.

The existence of Mars as a wandering object in the night sky was recorded by the ancient Egyptian astronomers
Egyptian astronomy
Egyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments...

 and by 1534 BCE they were familiar with the retrograde motion
Retrograde motion
Retrograde motion is motion in the direction opposite to the movement of something else, and is the contrary of direct or prograde motion. This motion can be the orbit of one body about another body or about some other point, or the rotation of a single body about its axis, or other phenomena such...

 of the planet. By the period of the Neo-Babylonian Empire
Neo-Babylonian Empire
The Neo-Babylonian Empire or Second Babylonian Empire was a period of Mesopotamian history which began in 626 BC and ended in 539 BC. During the preceding three centuries, Babylonia had been ruled by their fellow Akkadian speakers and northern neighbours, Assyria. Throughout that time Babylonia...

, the Babylonian astronomers were making regular records of the positions of the planets and systematic observations of their behavior. For Mars, they knew that the planet made 37 synodic periods, or 42 circuits of the zodiac, every 79 years. They also invented arithmetic methods for making minor corrections to the predicted positions of the planets.

In the fourth century BCE, Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 noted that Mars disappeared behind the Moon during an occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

, indicating the planet was farther away. Ptolemy
Ptolemy
Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

, a Greek living in Alexandria
Alexandria
Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

, attempted to address the problem of the orbital motion of Mars. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection Almagest
Almagest
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...

, which became the authoritative treatise on Western astronomy for the next fourteen centuries. Literature from ancient China confirms that Mars was known by Chinese astronomers
Chinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...

 by no later than the fourth century BCE. In the fifth century CE, the Indian astronomical text Surya Siddhanta
Surya Siddhanta
The Surya Siddhanta is one of the earliest siddhanta in archeo-astronomy of the Hindus by an unknown author. It describes the archeo-astronomy theories, principles and methods of the ancient Hindus. This siddhanta is supposed to be the knowledge that the Sun god gave to an Asura called Maya. Asuras...

estimated the diameter of Mars.

During the seventeenth century, Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...

 measured the diurnal parallax of Mars that Johannes Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...

 used to make a preliminary calculation of the relative distance to the planet. When the telescope became available, the diurnal parallax of Mars was again measured in an effort to determine the Sun-Earth distance. This was first performed by Giovanni Domenico Cassini
Giovanni Domenico Cassini
This article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...

 in 1672. The early parallax measurements were hampered by the quality of the instruments. The only occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

 of Mars by Venus observed was that of October 13, 1590, seen by Michael Maestlin
Michael Maestlin
Michael Maestlin was a German astronomer and mathematician, known for being the mentor of Johannes Kepler.-Career:...

 at Heidelberg
Heidelberg
-Early history:Between 600,000 and 200,000 years ago, "Heidelberg Man" died at nearby Mauer. His jaw bone was discovered in 1907; with scientific dating, his remains were determined to be the earliest evidence of human life in Europe. In the 5th century BC, a Celtic fortress of refuge and place of...

. In 1610, Mars was viewed by Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

, who was first to see it via telescope. The first person to draw a map of Mars that displayed any terrain features was the Dutch astronomer Christiaan Huygens.

Martian "canals"


By the 19th century, the resolution of telescopes reached a level sufficient for surface features to be identified. In September 1877, a perihelic opposition of Mars occurred on September 5. In that year, Italian astronomer Giovanni Schiaparelli
Giovanni Schiaparelli
Giovanni Virginio Schiaparelli was an Italian astronomer and science historian. He studied at the University of Turin and Berlin Observatory. In 1859-1860 he worked in Pulkovo Observatory and then worked for over forty years at Brera Observatory...

 used a 22 cm telescope in Milan
Milan
Milan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...

 to help produce the first detailed map of Mars. These maps notably contained features he called canali, which were later shown to be an optical illusion
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...

. These canali were supposedly long straight lines on the surface of Mars to which he gave names of famous rivers on Earth. His term, which means "channels" or "grooves", was popularly mistranslated in English as "canals".

Influenced by the observations, the orientalist Percival Lowell
Percival Lowell
Percival Lawrence Lowell was a businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death...

 founded an observatory
Lowell Observatory
Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....

 which had a 300 and 450 mm telescope. The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. He published several books on Mars and life on the planet, which had a great influence on the public. The canali were also found by other astronomers, like Henri Joseph Perrotin and Louis Thollon in Nice
Nice
Nice is the fifth most populous city in France, after Paris, Marseille, Lyon and Toulouse, with a population of 348,721 within its administrative limits on a land area of . The urban area of Nice extends beyond the administrative city limits with a population of more than 955,000 on an area of...

, using one of the largest telescopes of that time.

The seasonal changes (consisting of the diminishing of the polar caps and the dark areas formed during Martian summer) in combination with the canals lead to speculation about life on Mars, and it was a long held belief that Mars contained vast seas and vegetation. The telescope never reached the resolution required to give proof to any speculations. As bigger telescopes were used, fewer long, straight canali were observed. During an observation in 1909 by Flammarion
Camille Flammarion
Nicolas Camille Flammarion was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and several works about Spiritism and related topics. He also published the magazine...

 with a 840 mm telescope, irregular patterns were observed, but no canali were seen.

Even in the 1960s articles were published on Martian biology, putting aside explanations other than life for the seasonal changes on Mars. Detailed scenarios for the metabolism and chemical cycles for a functional ecosystem have been published.

It was not until spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 visited the planet during NASA's Mariner missions
Mariner program
The Mariner program was a program conducted by the American space agency NASA that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1963 to 1973...

 in the 1960s that these myths were dispelled. The results of the Viking life-detection experiments started an intermission in which the hypothesis of a hostile, dead planet was generally accepted.

Some maps of Mars were made using the data from these missions, but it was not until the Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

 mission, launched in 1996 and operated until late 2006, that complete, extremely detailed maps of the martian topography, magnetic field and surface minerals were obtained. These maps are now available online, for example, at Google Mars
Google Mars
Google Mars was at first an in-browser version of Google Maps which provides a visible imagery view, like Google Moon, as well as infrared imagery and shaded relief of the planet Mars. Users can toggle between the elevation, visible, and infrared data, in the same manner as switching between map,...

.

In culture



Mars is named after the Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 god of war
Mars (mythology)
Mars was the Roman god of war and also an agricultural guardian, a combination characteristic of early Rome. He was second in importance only to Jupiter, and he was the most prominent of the military gods worshipped by the Roman legions...

. In different cultures, Mars represents masculinity and youth. Its symbol, a circle with an arrow pointing out to the upper right, is also used as a symbol for the male gender.

Mars has been featured in science fiction media, and one theme is intelligent "Martians", responsible for the speculated "canals" and "faces" on the planet. Another theme is Mars being a future colony of the Earth, or human expedition.

The many failures in Mars exploration probes resulted in a satirical counter-culture blaming the failures on an Earth-Mars "Bermuda Triangle
Bermuda Triangle
The Bermuda Triangle, also known as the Devil's Triangle, is a region in the western part of the North Atlantic Ocean where a number of aircraft and surface vessels allegedly disappeared under mysterious circumstances....

", a Mars "Curse", or a "Great Galactic Ghoul" that feeds on Martian spacecraft.

Intelligent "Martians"



The popular idea that Mars was populated by intelligent Martian
Martian
As an adjective, the term martian is used to describe anything pertaining to the planet Mars.However, a Martian is more usually a hypothetical or fictional native inhabitant of the planet Mars. Historically, life on Mars has often been hypothesized, although there is currently no solid evidence of...

s exploded in the late 19th century. Schiaparelli's
Giovanni Schiaparelli
Giovanni Virginio Schiaparelli was an Italian astronomer and science historian. He studied at the University of Turin and Berlin Observatory. In 1859-1860 he worked in Pulkovo Observatory and then worked for over forty years at Brera Observatory...

 "canali" observations combined with Percival Lowell's
Percival Lowell
Percival Lawrence Lowell was a businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death...

 books on the subject put forward the standard notion of a planet that was a drying, cooling, dying world with ancient civilizations constructing irrigation works.
Many other observations and proclamations by notable personalities added to what has been termed "Mars Fever". In 1899 while investigating atmospheric radio noise using his receivers in his Colorado Springs lab, inventor Nikola Tesla
Nikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...

 observed repetitive signals that he later surmised might have been radio communications coming from another planet, possibly Mars. In a 1901 interview Tesla said:

It was some time afterward when the thought flashed upon my mind that the disturbances I had observed might be due to an intelligent control. Although I could not decipher their meaning, it was impossible for me to think of them as having been entirely accidental. The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another.


Tesla's theories gained support from Lord Kelvin who, while visiting the United States in 1902, was reported to have said that he thought Tesla had picked up Martian signals being sent to the United States. Kelvin "emphatically" denied this report shortly before departing America: "What I really said was that the inhabitants of Mars, if there are any, were doubtless able to see New York, particularly the glare of the electricity."

In a New York Times article in 1901, Edward Charles Pickering
Edward Charles Pickering
Edward Charles Pickering was an American astronomer and physicist, brother of William Henry Pickering.Along with Carl Vogel, Pickering discovered the first spectroscopic binary stars. He wrote Elements of Physical Manipulations .Pickering attended Boston Latin School, and received his B.S. from...

, director of the Harvard College Observatory
Harvard College Observatory
The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...

, said that they had received a telegram from Lowell Observatory
Lowell Observatory
Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....

 in Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

 that seemed to confirm that Mars was trying to communicate with the Earth.

Early in December 1900, we received from Lowell Observatory in Arizona a telegram that a shaft of light had been seen to project from Mars (the Lowell observatory makes a specialty of Mars) lasting seventy minutes. I wired these facts to Europe and sent out neostyle copies through this country. The observer there is a careful, reliable man and there is no reason to doubt that the light existed. It was given as from a well-known geographical point on Mars. That was all. Now the story has gone the world over. In Europe it is stated that I have been in communication with Mars, and all sorts of exaggerations have spring up. Whatever the light was, we have no means of knowing. Whether it had intelligence or not, no one can say. It is absolutely inexplicable.


Pickering later proposed creating a set of mirrors in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

 with the intention of signaling Martians.

In recent decades, the high resolution mapping of the surface of Mars, culminating in Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

, revealed no artifacts of habitation by 'intelligent' life, but pseudoscientific speculation about intelligent life on Mars continues from commentators such as Richard C. Hoagland
Richard C. Hoagland
Richard Charles Hoagland, is an American author and a proponent of various conspiracy theories about NASA, lost alien civilizations on the Moon and on Mars and other related topics....

. Reminiscent of the canali controversy, some speculations are based on small scale features perceived in the spacecraft images, such as 'pyramids' and the 'Face on Mars'. Planetary astronomer Carl Sagan
Carl Sagan
Carl Edward Sagan was an American astronomer, astrophysicist, cosmologist, author, science popularizer and science communicator in astronomy and natural sciences. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books...

 wrote:
Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears.


The depiction of Mars in fiction has been stimulated by its dramatic red color and by nineteenth century scientific speculations that its surface conditions not only might support life, but intelligent life. Thus originated a large number of science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 scenarios, among which is H. G. Wells
H. G. Wells
Herbert George Wells was an English author, now best known for his work in the science fiction genre. He was also a prolific writer in many other genres, including contemporary novels, history, politics and social commentary, even writing text books and rules for war games...

' The War of the Worlds, published in 1898, in which Martians seek to escape their dying planet by invading Earth. A subsequent US radio adaptation of The War of the Worlds
The War of the Worlds (radio)
The War of the Worlds was an episode of the American radio drama anthology series Mercury Theatre on the Air. It was performed as a Halloween episode of the series on October 30, 1938, and aired over the Columbia Broadcasting System radio network. Directed and narrated by actor and future filmmaker...

 on October 30, 1938 by Orson Welles
Orson Welles
George Orson Welles , best known as Orson Welles, was an American film director, actor, theatre director, screenwriter, and producer, who worked extensively in film, theatre, television and radio...

 was presented as a live news broadcast, and became notorious for causing a public panic when many listeners mistook it for the truth.

Influential works included Ray Bradbury
Ray Bradbury
Ray Douglas Bradbury is an American fantasy, horror, science fiction, and mystery writer. Best known for his dystopian novel Fahrenheit 451 and for the science fiction stories gathered together as The Martian Chronicles and The Illustrated Man , Bradbury is one of the most celebrated among 20th...

's The Martian Chronicles
The Martian Chronicles
The Martian Chronicles is a 1950 science fiction short story collection by Ray Bradbury that chronicles the colonization of Mars by humans fleeing from a troubled and eventually atomically devastated Earth, and the conflict between aboriginal Martians and the new colonists...

, in which human explorers accidentally destroy a Martian civilization, Edgar Rice Burroughs
Edgar Rice Burroughs
Edgar Rice Burroughs was an American author, best known for his creation of the jungle hero Tarzan and the heroic Mars adventurer John Carter, although he produced works in many genres.-Biography:...

' Barsoom series
Barsoom
Barsoom is a fictional representation of the planet Mars created by American pulp fiction author Edgar Rice Burroughs, who wrote close to 100 action adventure stories in various genres in the first half of the 20th century, and is now best known as the creator of the character Tarzan...

, C. S. Lewis
C. S. Lewis
Clive Staples Lewis , commonly referred to as C. S. Lewis and known to his friends and family as "Jack", was a novelist, academic, medievalist, literary critic, essayist, lay theologian and Christian apologist from Belfast, Ireland...

' novel Out of the Silent Planet
Out of the Silent Planet
Out of the Silent Planet is the first novel of a science fiction trilogy written by C. S. Lewis, sometimes referred to as the Space Trilogy, Ransom Trilogy or Cosmic Trilogy. The other volumes are Perelandra and That Hideous Strength, and a fragment of a sequel was published posthumously as The...

(1938), and a number of Robert A. Heinlein
Robert A. Heinlein
Robert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...

 stories before the mid-sixties.

Author Jonathan Swift
Jonathan Swift
Jonathan Swift was an Irish satirist, essayist, political pamphleteer , poet and cleric who became Dean of St...

 made reference to the moons of Mars, about 150 years before their actual discovery by Asaph Hall
Asaph Hall
Asaph Hall III was an American astronomer who is most famous for having discovered the moons of Mars in 1877...

, detailing reasonably accurate descriptions of their orbits, in the 19th chapter of his novel Gulliver's Travels
Gulliver's Travels
Travels into Several Remote Nations of the World, in Four Parts. By Lemuel Gulliver, First a Surgeon, and then a Captain of Several Ships, better known simply as Gulliver's Travels , is a novel by Anglo-Irish writer and clergyman Jonathan Swift that is both a satire on human nature and a parody of...

.

A comic figure of an intelligent Martian, Marvin the Martian
Marvin the Martian
Marvin the Martian is a fictional character appearing in the Looney Tunes cartoons. Marvin's likeness appears in miniature on the Spirit rover on Mars.-Conception and creation:...

, appeared on television in 1948 as a character in the Looney Tunes
Looney Tunes
Looney Tunes is a Warner Bros. animated cartoon series. It preceded the Merrie Melodies series and was Warner Bros.'s first animated theatrical series. Since its first official release, 1930's Sinkin' in the Bathtub, the series has become a worldwide media franchise, spawning several television...

 animated cartoons of Warner Brothers, and has continued as part of popular culture to the present.

After the Mariner
Mariner program
The Mariner program was a program conducted by the American space agency NASA that launched a series of robotic interplanetary probes designed to investigate Mars, Venus and Mercury from 1963 to 1973...

 and Viking
Viking program
The Viking program consisted of a pair of American space probes sent to Mars, Viking 1 and Viking 2. Each spacecraft was composed of two main parts, an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface...

 spacecraft had returned pictures of Mars as it really is, an apparently lifeless and canal-less world, these ideas about Mars had to be abandoned and a vogue for accurate, realist depictions of human colonies on Mars developed, the best known of which may be Kim Stanley Robinson
Kim Stanley Robinson
Kim Stanley Robinson is an American science fiction writer known for his award-winning Mars trilogy. His work delves into ecological and sociological themes regularly, and many of his novels appear to be the direct result of his own scientific fascinations, such as the fifteen years of research...

's Mars trilogy
Mars trilogy
The Mars trilogy is a series of award-winning science fiction novels by Kim Stanley Robinson that chronicles the settlement and terraforming of the planet Mars through the intensely personal and detailed viewpoints of a wide variety of characters spanning almost two centuries...

. Pseudo-scientific speculations about the Face on Mars and other enigmatic landmarks spotted by space probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...

s have meant that ancient civilizations continue to be a popular theme in science fiction, especially in film.

The theme of a Martian colony that fights for independence from Earth is a major plot element in the novels of Greg Bear
Greg Bear
Gregory Dale Bear is an American science fiction and mainstream author. His work has covered themes of galactic conflict , artificial universes , consciousness and cultural practices , and accelerated evolution...

 as well as the movie Total Recall
Total Recall
Total Recall is a 1990 American science fiction action film. The film stars Arnold Schwarzenegger, Rachel Ticotin, Sharon Stone, Michael Ironside, Ronny Cox & Mel Johnson, Jr.. It is based on the Philip K. Dick story “We Can Remember It for You Wholesale”...

(based on a short story by Philip K. Dick
Philip K. Dick
Philip Kindred Dick was an American novelist, short story writer and essayist whose published work is almost entirely in the science fiction genre. Dick explored sociological, political and metaphysical themes in novels dominated by monopolistic corporations, authoritarian governments and altered...

) and the television series Babylon 5
Babylon 5
Babylon 5 is an American science fiction television series created, produced and largely written by J. Michael Straczynski. The show centers on a space station named Babylon 5: a focal point for politics, diplomacy, and conflict during the years 2257–2262...

. Some video games also use this element, including Red Faction
Red Faction
Red Faction is a first-person shooter video game developed by Volition, Inc. and published by THQ. It was released for the PlayStation 2, Microsoft Windows and Mac in 2001. A version for the Nokia N-Gage was developed by Monkeystone Games. The game was also re-developed as a top-down shooter for...

and the Zone of the Enders
Zone of the Enders
The soundtrack to Zone of the Enders was released April 25, 2001 on the album Zone of the Enders Z.O.E Original Soundtrack by Konami Music Entertainment. Almost all the music was composed by the trio , and . Also, composed "Global 2 " and , "City ". The theme song "KISS ME SUNLIGHTS" was composed...

series. Mars (and its moons) were also the setting for the popular Doom video game franchise and the later Martian Gothic.

Timeline


Timeline based on one by NASA Goddard Space Flight Center (up to 2011)
Mission Launch Note
Marsnik 1 (Mars 1960A) 10 October 1960 Attempted Mars Flyby (Launch Failure)
Marsnik 2 (Mars 1960B) 14 October 1960 Attempted Mars Flyby (Launch Failure)
Sputnik 22
Sputnik 22
Mars 2MV-4 No.1 also known as Sputnik 22 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Mars programme, and was intended to make a flyby of Mars, and transmit images of the planet back to Earth. Due to a problem with the rocket which launched it, it was destroyed in...

 
24 October 1962 Attempted Mars Flyby
Mars 1
Mars 1
Mars 1, also known as 1962 Beta Nu 1, Mars 2MV-4 and Sputnik 23, was an automatic interplanetary station launched in the direction of Mars on November 1, 1962, the first of the Soviet Mars probe program, with the intent of flying by the planet at a distance of about 11,000 km...

 
1 November 1962 Mars Flyby (Contact Lost)
Sputnik 24
Sputnik 24
Mars 2MV-3 No.1 also known as Sputnik 24 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Mars programme, and was intended to land on the surface of Mars. Due to a problem with the rocket which launched it, it did not depart low Earth orbit, and it decayed several...

 
4 November 1962 Attempted Mars Lander
Mariner 3
Mariner 3
Mariner 3 and 4 were identical spacecraft of the Mariner program designed to carry out the first flybys of Mars and obtain photographs of the planet's surface. Mariner 3 was launched on November 5, 1964 from Cape Canaveral Air Force Station Launch Complex 13, but the shroud encasing the spacecraft...

 
5 November 1964 Attempted Mars Flyby
Mariner 4
Mariner 4
Mariner 4 was the fourth in a series of spacecraft, launched on November 28, 1964, intended for planetary exploration in a flyby mode and performed the first successful flyby of the planet Mars, returning the first pictures of the Martian surface...

 
28 November 1964 Mars Flyby
Zond 2
Zond 2
Zond 2, a member of the Soviet Zond program, was the fifth Soviet spacecraft to attempt a flyby of Mars. Zond-2 carried a phototelevision camera of the same type later used to photograph the Moon on Zond 3. The camera system also included two ultraviolet spectrometers...

 
30 November 1964 Mars Flyby (Contact Lost)
Zond 3
Zond 3
Zond 3 was a member of the Soviet Zond program sharing designation Zond, while being part of Mars 3MV project. It was unrelated to Zond spacecraft designed for manned circumlunar mission . Zond 3 completed a successful Lunar flyby, taking a number of good quality photographs for its time...

 
18 July 1965 Lunar Flyby, Mars Test Vehicle
Mariner 6  25 February 1969 Mars Flyby
Mariner 7  27 March 1969 Mars Flyby
Mars 1969A
Mars 1969A
Mars 2M No.521, also known as Mars M-69 No.521 and sometimes identified by NASA as Mars 1969A, was a Soviet spacecraft which was lost in a launch failure in 1969. It consisted of an orbiter and a lander. The spacecraft was intended to image the surface of Mars using three cameras, with images being...

 
27 March 1969 Attempted Mars Orbiter (Launch Failure)
Mars 1969B
Mars 1969B
Mars 2M No.522, also known as Mars M-69 No.522 and sometimes identified by NASA as Mars 1969B, was a Soviet spacecraft which was lost in a launch failure in 1969. It consisted of an orbiter and a lander. The spacecraft was intended to image the surface of Mars using three cameras, with images being...

 
2 April 1969 Attempted Mars Orbiter (Launch Failure)
Mariner 8
Mariner 8
Mariner-H, also commonly known as Mariner 8, was part of the Mariner Mars 71 project. It was intended to go into Mars orbit and return images and data.-Mission description:...

 
8 May 1971 Attempted Mars Flyby (Launch Failure)
Cosmos 419
Cosmos 419
Kosmos 419 was launched by the Soviet Union on May 10, 1971. Mars was at its closest to Earth since 1956 and, in May that year, both the Soviet Union and the United States made new attempts to reach the Red Planet. The payload however failed to separate from the fourth stage of the launch vehicle,...

 
10 May 1971 Attempted Mars Orbiter/Lander
Mars 2
Mars 2
The Mars program was a series of Mars unmanned landers and orbiters launched by the Soviet Union in the early 1970s.The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with an orbiter and an attached lander; they were the first human artifacts to impact the surface of Mars...

 
19 May 1971 Mars Orbiter/ Attempted Lander
Mars 3
Mars 3
The Mars 3 was an unmanned space probe of the Mars program, a series of unmanned Mars landers and orbiters launched by the Soviet Union in the early 1970s....

 
28 May 1971 Mars Orbiter/ Lander
Mariner 9
Mariner 9
Mariner 9 was a NASA space orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 13 of the same year, becoming the first spacecraft to orbit...

 
30 May 1971 Mars Orbiter
Mars 4  21 July 1973 Mars Flyby (Attempted Mars Orbiter)
Mars 5  25 July 1973 Mars Orbiter
Mars 6  5 August 1973 Mars Lander (Contact Lost)
Mars 7  9 August 1973 Mars Flyby (Attempted Mars Lander)
Viking 1
Viking 1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and until May 19, 2010 held the record for the second longest Mars surface mission of 6 years and 116 days .- Mission :Following...

 
20 August 1975 Mars Orbiter and Lander
Viking 2
Viking 2
The Viking 2 mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the Viking 1 mission. The Viking 2 lander operated on the surface for 1,281 Mars days and was turned off on 11 April 1980 when its batteries failed...

 
9 September 1975 Mars Orbiter and Lander
Phobos 1  7 July 1988 Attempted Mars Orbiter/Phobos Landers
Phobos 2  12 July 1988 Mars Orbiter/Attempted Phobos Landers
Mars Observer
Mars Observer
The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...

 
25 September 1992 Attempted Mars Orbiter (Contact Lost)
Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...

 
07 November 1996 Mars Orbiter
Mars 96
Mars 96
Mars 96 was a failed Mars mission launched in 1996 to investigate Mars by the Russian Space Forces and not directly related to the Soviet Mars probe program of the same name. After failure of the second fourth-stage burn, the probe assembly re-entered the Earth's atmosphere, breaking up over a...

 
16 November 1996 Attempted Mars Orbiter/Landers
Mars Pathfinder
Mars Pathfinder
Mars Pathfinder was an American spacecraft that landed a base station with roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight wheeled robotic rover named Sojourner.Launched on December 4, 1996 by NASA aboard a Delta II booster a...

 
04 December 1996 Mars Lander and Rover
Nozomi (Planet-B) 3 July 1998 Mars Orbiter
Mars Climate Orbiter
Mars Climate Orbiter
The Mars Climate Orbiter was a 338 kilogram robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor '98 program, for Mars Polar Lander...

 
11 December 1998 Attempted Mars Orbiter
Mars Polar Lander
Mars Polar Lander
The Mars Polar Lander, also referred to as the Mars Surveyor '98 Lander, was a 290-kilogram robotic spacecraft lander, launched by NASA on January 3, 1999, to study the soil and climate of Planum Australe, a region near the south pole on Mars, as part of the Mars Surveyor '98 mission...

 
3 January 1999 Attempted Mars Lander
Deep Space 2 (DS2)  3 January 1999 Attempted Mars Penetrators
2001 Mars Odyssey
2001 Mars Odyssey
2001 Mars Odyssey is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectrometers and electronic imagers to hunt for evidence of past or...

 
7 April 2001 Mars Orbiter
Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...

 
2 June 2003 Mars Orbiter and Lander
Spirit (MER-A)
Spirit rover
Spirit, MER-A , is a robotic rover on Mars, active from 2004 to 2010. It was one of two rovers of NASA's ongoing Mars Exploration Rover Mission. It landed successfully on Mars at 04:35 Ground UTC on January 4, 2004, three weeks before its twin, Opportunity , landed on the other side of the planet...

 
10 June 2003 Mars Rover
Opportunity (MER-B)
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...

 
7 July 2003 Mars Rover
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...

 
10 August 2005 Mars Orbiter
Phoenix
Phoenix (spacecraft)
Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...

 
04 August 2007 Mars Scout Lander
Phobos-Grunt
Phobos-Grunt
Fobos-Grunt or Phobos-Grunt was an attempted Russian sample return mission to Phobos, one of the moons of Mars. It was launched on 9 November 2011 at 02:16 local time from the Baikonur Cosmodrome, but subsequent rocket burns intended to set the craft on a course for Mars failed, leaving it...

 
08 November 2011 Martian Moon Phobos Lander
Yinghuo-1  08 November 2011 Mars Orbiter
Mars Science Laboratory
Mars Science Laboratory
The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...

 
26 November 2011 Mars Rover
MAVEN
Maven
A maven is a trusted expert in a particular field, who seeks to pass knowledge on to others. The word maven comes from Hebrew, via Yiddish, and means one who understands, based on an accumulation of knowledge.-History:...

 
18 November 2013 (planned) Mars Scout Mission Orbiter

See also



  • Colonization of Mars
    Colonization of Mars
    The colonization of Mars by humans is the focus of speculation and serious study because the surface conditions and availability of water on Mars make it arguably the most hospitable planet in the solar system other than Earth...

  • Darian calendar
    Darian calendar
    The Darian Calendar better known as the "Calendar of Adam" is a proposed system of time-keeping designed to serve the needs of any possible future human settlers on the planet Mars...

    —system of time-keeping
  • Extraterrestrial life
    Extraterrestrial life
    Extraterrestrial life is defined as life that does not originate from Earth...

  • List of artificial objects on Mars
  • List of chasmata on Mars
  • List of craters on Mars
  • List of valles on Mars
  • Terraforming of Mars
    Terraforming of Mars
    The terraforming of Mars is the hypothetical process by which the climate, surface, and known properties of Mars would be deliberately changed with the goal of making it habitable by humans and other terrestrial life, thus providing the possibility of safe and sustainable colonization of large...

  • 2007 WD5
    2007 WD5
    ' is a diameter Apollo class near-Earth object and a Mars-crosser asteroid discovered on November 20, 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance...

    —asteroid that had a possible impact with Mars on January 30, 2008
  • Seasonal flows on warm Martian slopes
    Seasonal flows on warm Martian slopes
    Observations from NASA's Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars. Research suggests that in the past there was liquid water flowing on the surface, creating large areas similar to Earth's oceans. However, the question remains as to where...


External links


  • Mars Exploration Program
  • On Mars: Exploration of the Red Planet 1958–1978 from the NASA History Office.
  • Mars Unearthed—Comparisons of terrains between Earth and Mars
  • Be on Mars—Anaglyphs from the Mars Rovers (3D)
  • Mars articles in Planetary Science Research Discoveries
  • Geody Mars—World's search engine that supports NASA World Wind
    NASA World Wind
    World Wind is an open-source virtual globe developed by NASA and the open source community for use on personal computers. Old versions need Microsoft Windows but the more recent Java version, , is cross platform and provides a suite of . The World Wind Java version was awarded in November 2009...

    , Celestia
    Celestia
    Celestia is a 3D astronomy program created by Chris Laurel. The program is based on the Hipparcos Catalogue and allows users to travel through an extensive universe, modeled after reality, at any speed, in any direction and at any time in history...

    , and other applications
  • Mars Society—The Mars Society
    Mars Society
    The Mars Society is an international space advocacy non-profit organization dedicated to promoting the human exploration and settlement of the planet Mars. It was founded by Robert Zubrin and others in 1998 and attracted the support of notable science fiction writers and filmmakers, including Kim...

    , an international organization dedicated to the study, exploration, and settlement of Mars.
  • NASA/JPL OnMars WMS Server for Mars Data—Work as Google Earth client overlays
  • New Papers about Martian Geomorphology


Media
  • Computer Simulation of a flyby through Mariner Valley
  • Movie of Mars at National Oceanic and Atmospheric Administration
  • Flight Into Mariner Valley—NASA/JPL/Arizona State University 3D flythrough of Valles Marineris
  • Mars Astronomy Cast
    Astronomy Cast
    Astronomy Cast is an educational nonprofit podcast discussing various topics in the field of astronomy. The specific subject matter of each episode shifts from week to week, ranging from planets and stars to cosmology and mythbusting...

     episode #52, includes full transcript
  • 15 Amazing Pictures of the Red Planet – slideshow at The Huffington Post
    The Huffington Post
    The Huffington Post is an American news website and content-aggregating blog founded by Arianna Huffington, Kenneth Lerer, and Jonah Peretti, featuring liberal minded columnists and various news sources. The site offers coverage of politics, theology, media, business, entertainment, living, style,...



Cartographic resources