Observations and explorations of Venus

Observations of the planet 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...

were first recorded by Babylon

Babylon

Babylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...

ian astronomers around 1600 BC and have continued into the present. The Maya

Maya civilization

The Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period The Maya is a Mesoamerican...

also kept records of the movements of Venus

Venus

and attached special importance to the planet. In 1610, 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...

was the first person to observe Venus

Venus

through 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...

, and discovered that it appears to undergo phases

Planetary phase

Planetary phase is the term used to describe the appearance of the illuminated section of a planet. Like lunar phases, the planetary phase depends on the relative position of the sun, the planet and the observer....

, supporting the heliocentric

Heliocentrism

Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...

model of planetary motions. Important later observations centered around rare transits of Venus, in which the planet passes across the face of 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...

as seen from 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...

. During one transit in 1761, Mikhail Lomonosov

Mikhail Lomonosov

Mikhail Vasilyevich Lomonosov was a Russian polymath, scientist and writer, who made important contributions to literature, education, and science. Among his discoveries was the atmosphere of Venus. His spheres of science were natural science, chemistry, physics, mineralogy, history, art,...

discovered that Venus

Venus

has an 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...

, and another transit in the 19th century allowed astronomers to calculate the distance from Earth to the Sun

Astronomical unit

An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

. In the early 1960s, astronomers studied Venus

Venus

by making radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

and microwave

Microwave

Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...

observations from Earth, which suggested Venus

Venus

has a surface temperature of several hundred kelvin

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

s.

The exploration of Venus

Venus

by space probes

Robotic spacecraft

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...

began shortly after the Space Age

Space exploration

Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....

, starting with the Soviet probe Venera 1

Venera 1

On February 12, 1961, 00:34:36 UTC, was the first planetary probe launched to Venus by the Soviet Union. The Venus-1 Automatic Interplanetary Station, or Venera 1, was a 643.5 kg probe consisting of a cylindrical body 1.05 metres in diameter topped by a dome, totalling 2.035 metres...

in 1961. The first successful Venus

Venus

probe was 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 Mariner 2

Mariner 2

Mariner 2 , an American space probe to Venus, was the first space probe to conduct a successful planetary encounter . The first successful spacecraft in the NASA Mariner program, it was a simplified version of the Block I spacecraft of the Ranger program and an exact copy of Mariner 1...

, which flew by the planet and confirmed its high surface temperatures. In 1966, Venera 3

Venera 3

Venera 3 was a Venera program space probe that was built and launched by the Soviet Union to explore the surface of Venus. It was launched on November 16, 1965 at 04:19 UTC from Baikonur, Kazakhstan....

became the first spacecraft to reach the surface of another planet when it crash-landed on Venus

Venus

. Its successor Venera 4

Venera 4

Venera 4 ) was a probe in the Soviet Venera program for the exploration of Venus. Venera-4 was the first successful probe to perform in-place analysis of the environment of another planet. It was also the first probe to land on another planet...

succeeded in returning data during its descent, reporting that the atmosphere of Venus

Atmosphere of Venus

The atmosphere of Venus is much denser and hotter than that of Earth. The temperature at the surface is 740 K , while the pressure is 93 bar. The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible...

was 95% carbon dioxide and the surface 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...

around 100 times greater than on 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...

. Venera 7

Venera 7

The Venera 7 was a Soviet spacecraft, part of the Venera series of probes to Venus. When it landed on the Venusian surface, it became the first man-made spacecraft to successfully land on another planet and to transmit data from there back to Earth.*Launch date/time: 1970 August 17 at 05:38...

made the first successful soft landing in 1970. In 1975, Venera 9

Venera 9

Venera 9 was a USSR unmanned space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 8, 1975 02:38:00 UTC and weighed 4,936 kg...

and 10

Venera 10

Venera 10 was a USSR unmanned space mission to Venus. It consisted of an orbiter and a lander. It launched on June 14, 1975 03:00:31 UTC.-Orbiter:The orbiter entered Venus orbit on October 23, 1975...

were the first spacecraft to enter an orbit around Venus, each also dispatching a lander to the surface. They were followed by several other NASA

NASA

and Soviet

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...

orbiter/lander missions during the late 1970s and 1980s, including Venera

Venera

The Venera series probes were developed by the Soviet Union between 1961 and 1984 to gather data from Venus, Venera being the Russian name for Venus...

s 11 through 16, Pioneer Venus, and Vega

Vega

Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...

. However, there have been fewer Venus

Venus

missions since the collapse of the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

. Between 1990 and 1994, NASA

NASA

's Magellan

Magellan

Magellan may refer to:*Ferdinand Magellan, a Portuguese explorer who led part of the first expedition around the world*Magellan , a progressive rock band*Magellan , a forerunner of the Excite web portal...

orbiter mapped 98% of the surface using radar. 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...

's Venus Express

Venus Express

Venus Express is the first Venus exploration mission of the European Space Agency. Launched in November 2005, it arrived at Venus in April 2006 and has been continuously sending back science data from its polar orbit around Venus. Equipped with seven science instruments, the main objective of the...

arrived in orbit around the planet in 2006, and is currently studying its atmosphere and surface characteristics.

Historical observations

Asia

One of the oldest surviving astronomical documents, from the Babylon

Babylon

Babylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...

ian library of Ashurbanipal

Ashurbanipal

Ashurbanipal |Ashur]] is creator of an heir"; 685 BC – c. 627 BC), also spelled Assurbanipal or Ashshurbanipal, was an Assyrian king, the son of Esarhaddon and the last great king of the Neo-Assyrian Empire...

around 1600 BC, is a 21-year record of the appearances of Venus

Venus

(which the early Babylonians called Nindaranna).

The ancient Sumer

Sumer

Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....

ians and Babylonians called Venus Dil-bat or Dil-i-pat; in Akkad

Akkad

The Akkadian Empire was an empire centered in the city of Akkad and its surrounding region in Mesopotamia....

ia it was the special star of the mother-god Ishtar

Ishtar

Ishtar is the Assyrian and Babylonian goddess of fertility, love, war, and sex. She is the counterpart to the Sumerian Inanna and to the cognate north-west Semitic goddess Astarte.-Characteristics:...

; and in Chinese

Chinese language

The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...

it is Jīn-xīng (金星), the planet of the metal element. In India, Venus is called Shukra Graha ("the planet Shukra") which is named after a powerful saint Shukra. The word Shukra is also associated with semen, or generation.

Maya

Venus was considered the most important celestial body observed by the Maya

Maya civilization

, who called it Chak ek, "the Great Star". The Mayans monitored the movements of Venus closely and observed it in daytime. The positions of Venus and other planets were thought to influence life on Earth, so Maya and other ancient Mesoamerican cultures timed wars and other important events based on their observations. In the Dresden Codex

Dresden Codex

The Dresden Codex, also known as the Codex Dresdensis, is a pre-Columbian Maya book of the eleventh or twelfth century of the Yucatecan Maya in Chichén Itzá. The Maya codex is believed to be a copy of an original text of some three or four hundred years earlier...

, the Maya included an almanac showing Venus's full cycle, in five sets of 584 days each (approximately eight years), after which the patterns repeated (since Venus has a synodic period of 583.92 days).

Greeks

Early Greeks

Ancient Greece

Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

thought that the evening and morning appearances of Venus represented two different objects, calling it Hesperus when it appeared in the western evening sky and Phosphorus when it appeared in the eastern morning sky. They eventually came to recognize that both objects were the same planet; Pythagoras

Pythagoras

Pythagoras of Samos was an Ionian Greek philosopher, mathematician, and founder of the religious movement called Pythagoreanism. Most of the information about Pythagoras was written down centuries after he lived, so very little reliable information is known about him...

is credited with this realization.

Phases

Because its orbit

Planetary orbit

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

takes it between the Earth and the Sun, Venus as seen from Earth exhibits visible phases

Planetary phase

in much the same manner as the Earth's Moon. Galileo Galilei

Galileo Galilei

was the first person to observe the phases of Venus in December 1610, an observation which supported Copernicus's then contentious heliocentric

Heliocentrism

description of the solar system. He also noted changes in the size of Venus's visible diameter when it was in different phases, suggesting that it was farther from Earth when it was full and nearer when it was a crescent. This observation strongly supported the heliocentric model. Venus (and also Mercury) is not visible from Earth when it is full, since at that time it is at superior conjunction, rising and setting concomitantly with the Sun and hence lost in the Sun's glare.

Venus is brightest when approximately 25% of its disk is illuminated; this typically occurs 37 days both before (in the evening sky) and after (in the morning sky), its inferior conjunction. Its greatest elongations occur approximately 70 days before and after inferior conjunction, at which time it is half full; between these two intervals Venus is actually visible in broad daylight, if the observer knows specifically where to look for it. The planet's period of retrograde motion is 20 days on either side of the inferior conjunction. In fact, through a telescope Venus at greatest elongation appears less than half full due to Schröter's effect first noticed in 1793 and shown in 1996 as due to its thick atmosphere.

On rare occasions, Venus can actually be seen in both the morning (before sunrise) and evening (after sunset) on the same day. This scenario arises when Venus is at its maximum separation from the 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...

and concomitantly at inferior conjunction; then one hemisphere (Northern or Southern) will be able to see it at both times. This opportunity presented itself most recently for Northern Hemisphere observers within a few days on either side of March 29, 2001, and for those in the Southern Hemisphere, on and around August 19, 1999. These respective events repeat themselves every eight years pursuant to the planet's synodic cycle.

Transit and early terrestrial observations

Transits of Venus

Transit of Venus

A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth, becoming visible against the solar disk. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun...

, when the planet crosses directly between the Earth and the Sun's visible disc, are rare astronomical events. The first time such a transit

Astronomical transit

The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...

was observed was on December 4, 1639 by Jeremiah Horrocks

Jeremiah Horrocks

Jeremiah Horrocks , sometimes given as Jeremiah Horrox , was an English astronomer who was the only person to predict, and one of only two people to observe and record, the transit of Venus of 1639.- Life and work :Horrocks was born in Lower Lodge, in...

and William Crabtree

William Crabtree

William Crabtree was an astronomer, mathematician, and merchant from Broughton, then a township near Manchester, which is now part of Salford, Greater Manchester, England...

. A transit in 1761 observed by Mikhail Lomonosov

Mikhail Lomonosov

provided the first evidence that Venus had an atmosphere, and the 19th-century observations of parallax

Parallax

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...

during its transits allowed the distance between the Earth and Sun to be accurately calculated for the first time. Transits can only occur either in early June or early December, these being the points at which Venus crosses the ecliptic (the orbital plane of the Earth), and occur in pairs at eight-year intervals, with each such pair more than a century apart. The previous pair of transits of Venus occurred in 1874 and 1882, and the current pair is in 2004 and 2012.

In the 19th century, many observers stated that Venus had a period of rotation of roughly 24 hours. 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...

was the first to predict a significantly slower rotation, proposing that Venus was tidally locked

Tidal locking

Tidal locking occurs when the gravitational gradient makes one side of an astronomical body always face another; for example, the same side of the Earth's Moon always faces the Earth. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner...

with the Sun (as he had also proposed for Mercury). While not actually true for either body, this was still a reasonably accurate estimate. The near-resonance between its rotation and its closest approach to Earth helped to create this impression, as Venus always seemed to be facing the same direction when it was in the best location for observations to be made. The rotation rate of Venus was first measured during the 1961 conjunction, observed by radar from a 26 m antenna at Goldstone, California, the Jodrell Bank

Jodrell Bank

The Jodrell Bank Observatory is a British observatory that hosts a number of radio telescopes, and is part of the Jodrell Bank Centre for Astrophysics at the University of Manchester...

Radio Observatory in the UK

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, and the Soviet

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

deep space facility in Eupatoria

Eupatoria

Yevpatoria or Eupatoria is a city in Crimea, Ukraine.-History:The first recorded settlement in the area, called Kerkinitis , was built by Greek colonists around 500 BC...

, Crimea

Crimea

Crimea , or the Autonomous Republic of Crimea , is a sub-national unit, an autonomous republic, of Ukraine. It is located on the northern coast of the Black Sea, occupying a peninsula of the same name...

. Accuracy was refined at each subsequent conjunction, primarily from measurements made from Goldstone and Eupatoria. The fact that rotation was retrograde was not confirmed until 1964.

Before radio observations in the 1960s, many believed that Venus contained a lush, Earth-like environment. This was due to the planet's size and orbital radius, which suggested a fairly Earth-like situation as well as to the thick layer of clouds which prevented the surface from being seen. Among the speculations on Venus were that it had a jungle-like environment or that it had oceans of either petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

or carbonated water. However, microwave observations by C. Mayer et al., indicated a high-temperature source (600 K). Strangely, millimetre-band observations made by A. D. Kuzmin indicated much lower temperatures. Two competing theories explained the unusual radio spectrum, one suggesting the high temperatures originated in the ionosphere, and another suggesting a hot planetary surface.

Terrestrial radar mapping

After the Moon, Venus was the second object 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...

to be explored by radar from the Earth. The first studies were carried out in 1961 at NASA

NASA

's Goldstone Observatory

Goldstone Deep Space Communications Complex

The Goldstone Deep Space Communications Complex — commonly called the Goldstone Observatory — is located in California's Mojave Desert. Operated by ITT Corporation for the Jet Propulsion Laboratory, its main purpose is to track and communicate with space missions. It includes the Pioneer...

, part of the Deep Space Network

Deep Space Network

The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...

. At successive inferior conjunctions, Venus was observed both by Goldstone and the National Astronomy and Ionosphere Center

Arecibo Observatory

The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...

in Arecibo

Arecibo

Arecibo may refer to:*Arecibo, Puerto Rico, a municipality located by the Atlantic Ocean*Arecibo Observatory, a very sensitive radio telescope located approximately south-southwest from the city of Arecibo...

. The studies carried out were similar to the earlier measurement of transits of the meridian

Meridian (astronomy)

This article is about the astronomical concept. For other uses of the word, see Meridian.In the sky, a meridian is an imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the...

, which had revealed in 1963 that the rotation of Venus was retrograde

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...

(it rotates in the opposite direction to that in which it orbits the Sun). The radar observations also allowed astronomers to determine that the rotation period

Rotation period

The rotation period of an astronomical object is the time it takes to complete one revolution around its axis of rotation relative to the background stars...

of Venus was 243.1 days, and that its axis of rotation was almost perpendicular to its orbital plane

Orbital plane (astronomy)

All of the planets, comets, and asteroids in the solar system are in orbit around the Sun. All of those orbits line up with each other making a semi-flat disk called the orbital plane. The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded...

. It was also established that the radius

Radius

In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...

of the planet was 6052 kilometres (3,760.5 mi), some 70 kilometres (43.5 mi) less than the best previous figure obtained with terrestrial telescopes.

Interest in the geological characteristics of Venus was stimulated by the refinement of imaging techniques between 1970 and 1985. Early radar observations suggested merely that the surface of Venus was more compacted than the dusty surface of the Moon. The first radar images taken from the Earth showed very bright (radar-reflective) highlands christened Alpha Regio

Alpha Regio

Alpha Regio is a region of the planet Venus extending for about 1500 kilometers centered at 22°S, 5°E.It was discovered and named by Dick Goldstein in 1964. The name was approved by the International Astronomical Union's Working Group for Planetary System Nomenclature between 1976 and 1979...

, Beta Regio

Beta Regio

Beta Regio is a region of the planet Venus known as a volcanic rise. Measuring about 3000 km, it constitutes a prominent upland region of Venus centered at ....

, and Maxwell Montes

Maxwell Montes

Maxwell Montes is a mountain massif on the planet Venus, part of which contains the highest point on the planet's surface.- General description :...

; improvements in radar techniques later achieved an image resolution of 1–2 kilometres.

Observation by spacecraft

There have been numerous unmanned missions to Venus. Ten Soviet

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

probes have achieved a soft landing on the surface, with up to 110 minutes of communication from the surface, all without return. Launch window

Launch window

Launch window is a term used in spaceflight to describe a time period in which a particular launch vehicle must be launched. If the rocket does not launch within the "window", it has to wait for the next window....

s occur every 19 months, and from 1962 to 1985, every window was utilized to launch reconnaissance probes.

Early flybys

On February 12, 1961, the Soviet spacecraft

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...

Venera 1

was the first probe

Robotic spacecraft

launched to another planet. An overheated orientation sensor caused it to malfunction, but Venera 1 was first to combine all the necessary features of an interplanetary spacecraft: solar panels, parabolic telemetry antenna, 3-axis stabilization, course-correction engine, and the first launch from parking orbit.

The first successful Venus probe was the American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

Mariner 2

spacecraft, which flew past Venus in 1962. A modified Ranger

Ranger program

The Ranger program was a series of unmanned space missions by the United States in the 1960s whose objective was to obtain the first close-up images of the surface of the Moon. The Ranger spacecraft were designed to take images of the lunar surface, returning those images until they were destroyed...

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...

probe, it established that Venus has practically no intrinsic 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;...

and measured the planet's temperature range as 490 to 590 K.

The Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

launched the Zond 1

Zond 1

Zond 1 was a member of the Soviet Zond program. It was the second Soviet research spacecraft to successfully reach Venus, although communications had failed by that time...

probe to Venus in 1964, but it malfunctioned sometime after its May 16 telemetry session.

During another American flyby in 1967, Mariner 5

Mariner 5

Mariner 5 was a spacecraft of the Mariner program that carried a complement of experiments to probe Venus' atmosphere by radio occultation, measure the hydrogen Lyman-alpha spectrum, and sample the solar particles and magnetic field fluctuations above the planet...

measured the strength of Venus's magnetic field

Magnetic field

. In 1974, Mariner 10

Mariner 10

Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...

swung by Venus on its way to Mercury and took ultraviolet photographs of the clouds, revealing the extraordinarily high wind speeds in the Venusian atmosphere.

Early landings

On March 1, 1966 the Venera 3

Venera 3

Soviet space probe

Space probe

crash-landed on Venus, becoming the first spacecraft to reach the surface of another planet. Its sister craft Venera 2

Venera 2

Venera 2 was a probe in the Soviet Venera program for the exploration of Venus.*Launch Date/Time: 1965 November 12 at 05:02:00 UTC*On-orbit Dry Mass: 963 kg...

had failed due to overheating shortly before completing its flyby mission.

The descent capsule of Venera 4

Venera 4

entered the atmosphere of Venus on October 18, 1967, making it the first probe to return direct measurements from another planet's atmosphere. The capsule measured temperature, pressure, density and performed 11 automatic chemical experiments to analyze the atmosphere. It discovered that the atmosphere of Venus was 95% carbon dioxide, and in combination with radio occultation data from the Mariner 5

Mariner 5

probe, showed that surface pressures were far greater than expected (75 to 100 atmospheres).

These results were verified and refined by the Venera 5

Venera 5

Venera 5 was a probe in the Soviet space program Venera for the exploration of Venus.Venera 5 was launched from a Tyazheliy Sputnik towards Venus to obtain atmospheric data...

and Venera 6

Venera 6

Venera 6 was a Soviet spacecraft, launched from a Tyazheliy Sputnik on January 10, 1969 towards Venus to obtain atmospheric data. It had an on-orbit dry mass of 1130 kg....

in May 1969. But thus far, none of these missions had reached the surface while still transmitting. Venera 4s battery ran out while still slowly floating through the massive atmosphere, and Venera 5 and 6 were crushed by high pressure 18 km (60,000 ft) above the surface.

The first successful landing on Venus was by Venera 7

Venera 7

on December 15, 1970. It remained in contact with Earth for 23 minutes, relaying surface temperatures of 455 °C to 475 °C (855 °F to 885 °F). Venera 8

Venera 8

Venera 8 was a probe in the Soviet Venera program for the exploration of Venus.Venera 8 was a Venus atmospheric probe and lander. Its instrumentation included temperature, pressure, and light sensors as well as an altimeter, gamma ray spectrometer, gas analyzer, and radio transmitters...

landed on July 22, 1972. In addition to pressure and temperature profiles, a photometer showed that the clouds of Venus formed a layer, ending over 22 miles above the surface. A gamma ray spectrometer

Gamma ray spectrometer

A Gamma-Ray Spectrometer, or , is an instrument for measuring the distribution of the intensity of gamma radiation versus the energy of each photon....

analyzed the chemical composition of the crust.

Venera 9 and 10

The Soviet probe Venera 9

Venera 9

Venera 9 was a USSR unmanned space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 8, 1975 02:38:00 UTC and weighed 4,936 kg...

entered orbit on October 22, 1975, becoming the first artificial satellite of Venus. A battery of cameras and spectrometers returned information about the planet's clouds, ionosphere and magnetosphere, as well as performing bi-static radar measurements of the surface. The 660 kg (1,455 lb) descent vehicle separated from Venera 9 and landed, taking the first pictures of the surface and analyzing the crust with a gamma ray spectrometer and a densitometer. During descent, pressure, temperature and photometric measurements were made, as well as backscattering and multi-angle scattering (nephelometer

Nephelometer

A nephelometer is a stationary or portable instrument for measuring suspended particulates in a liquid or gas colloid. A nephelometer measures suspended particulates by employing a light beam and a light detector set to one side of the source beam. Particle density is then a function of the...

) measurements of cloud density. It was discovered that the clouds of Venus are formed in three distinct layers. On October 25, Venera 10

Venera 10

arrived and carried out a similar program of study.

Pioneer Venus

In 1978, NASA

NASA

sent two Pioneer

Pioneer Venus project

The Pioneer mission to Venus consisted of two components, launched separately. Pioneer Venus 1 or Pioneer Venus Orbiter was launched in 1978 and studied the planet for more than a decade after orbital insertion in 1978. Pioneer Venus 2 or Pioneer Venus Multiprobe sent four small probes into the...

spacecraft to Venus. The Pioneer mission consisted of two components, launched separately: an orbiter and a multiprobe. The Pioneer Venus Multiprobe carried one large and three small atmospheric probes. The large probe was released on November 16, 1978 and the three small probes on November 20. All four probes entered the Venusian atmosphere on December 9, followed by the delivery vehicle. Although not expected to survive the descent through the atmosphere, one probe continued to operate for 45 minutes after reaching the surface. The Pioneer Venus Orbiter was inserted into an elliptical orbit around Venus on December 4, 1978. It carried 17 experiments and operated until the fuel used to maintain its orbit was exhausted and atmospheric entry destroyed the spacecraft in August 1992.

Further Soviet missions

Also in 1978, Venera 11

Venera 11

The Venera 11 was a USSR unmanned space mission part of the Venera program to explore the planet Venus. Venera 11 was launched on 9 September 1978 at 3:25:39 UTC....

and Venera 12

Venera 12

The Venera 12 was an USSR unmanned space mission to explore the planet Venus. Venera 12 was launched on 14 September 1978 at 02:25:13 UTC. Separating from its flight platform on December 19, 1978, the lander entered the Venus atmosphere two days later at 11.2 km/s. During the descent, it...

flew past Venus, dropping descent vehicles on December 21 and December 25 respectively. The landers carried colour cameras and a soil drill and analyzer, which unfortunately malfunctioned. Each lander made measurements with a nephelometer

Nephelometer

, mass spectrometer, gas chromatograph, and a cloud-droplet chemical analyzer using X-ray fluorescence

X-ray fluorescence

X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...

that unexpectedly discovered a large proportion of chlorine in the clouds, in addition to sulfur. Strong lightning

Lightning

Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

activity was also detected.

In 1981, the Soviet Venera 13

Venera 13

Venera 13 was a probe in the Soviet Venera program for the exploration of Venus.Venera 13 and 14 were identical spacecraft built to take advantage of the 1981 Venus launch opportunity and launched 5 days apart, Venera 13 on 1981-10-30 at 06:04:00 UTC and Venera 14 on 1981-11-04 at 05:31:00 UTC,...

sent the first colour image of Venus's surface and analysed the X-ray fluorescence

X-ray fluorescence

X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...

of an excavated soil sample. The probe operated for a record 127 minutes on the planet's hostile surface. Also in 1981, the Venera 14

Venera 14

Venera 14 was a probe in the Soviet Venera program for the exploration of Venus.Venera 14 was identical to the Venera 13 spacecraft and built to take advantage of the 1981 Venus launch opportunity and launched 5 days apart...

lander detected possible seismic

Seismology

Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...

activity in the planet's crust

Crust

Crust may refer to:* Crust * The Crust, television seriesPhysical sciences:* Crust , at least continent-wide structure* Soil crust, local biology-sensitive structureFood:* Crust, dense surface layer of bread...

.

In December 1984, during the apparition of Halley's Comet, the Soviet Union launched the two Vega

Vega program

The Vega program was a series of Venus missions which also took advantage of the appearance of Comet Halley in 1986. Vega 1 and Vega 2 were unmanned spacecraft launched in a cooperative effort among the Soviet Union and Austria, Bulgaria, Hungary, the German Democratic Republic, Poland,...

probes to Venus.
Vega 1

Vega 1

Vega 1 is a Soviet space probe part of the Vega program. The spacecraft was a development of the earlier Venera craft...

and Vega 2

Vega 2

Vega 2 is a Soviet space probe part of the Vega program. The spacecraft was a development of the earlier Venera craft. They were designed by Babakin Space Center and constructed as 5VK by Lavochkin at Khimki...

encountered Venus in June 1985, each deploying a lander and an instrumented helium balloon. The balloon-borne aerostat

Aerostat

An aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...

probes floated at about 53 km altitude for 46 and 60 hours respectively, traveling about 1/3 of the way around the planet and allowing scientists to study the dynamics of the most active part of Venus's atmosphere. These measured wind speed, temperature, pressure and cloud density. More turbulence and convection activity than expected was discovered, including occasional plunges of 1 to 3 km in downdrafts.

The landing vehicles carried experiments focusing on cloud aerosol composition and structure. Each carried an ultraviolet absorption spectrometer, aerosol particle-size analyzers, and devices for collecting aerosol material and analyzing it with a mass spectrometer, a gas chromatograph, and an X-ray fluorescence spectrometer. The upper two layers of the clouds were found to be sulfuric acid droplets, but the lower layer is probably composed of phosphoric acid solution. The crust of Venus was analyzed with the soil drill experiment and a gamma ray spectrometer. As the landers carried no cameras on board, no images were returned from the surface. They would be the last probes to land on Venus for decades. The Vega spacecraft continued to rendezvous with Halley's Comet nine months later, bringing an additional 14 instruments and cameras for that mission.

Venera 15 and 16

In October 1983, Venera 15

Venera 15

Venera 15 was a spacecraft sent to Venus by the Soviet Union. This unmanned orbiter was to map the surface of Venus using high resolution imaging systems...

and Venera 16

Venera 16

Venera 16 was a spacecraft sent to Venus by the Soviet Union. This unmanned orbiter was to map the surface of Venus using high resolution imaging systems...

entered polar orbits around Venus. The images had a 1–2 kilometre (0.6–1.2 mile) resolution, comparable to those obtained by the best Earth radars. Venera 15 analyzed and mapped the upper atmosphere with an infrared Fourier spectrometer. From November 11 to July 10, both satellites mapped the northern third of the planet with synthetic aperture radar

Synthetic aperture radar

Synthetic-aperture radar is a form of radar whose defining characteristic is its use of relative motion between an antenna and its target region to provide distinctive long-term coherent-signal variations that are exploited to obtain finer spatial resolution than is possible with conventional...

. These results provided the first detailed understanding of the surface geology of Venus, including the discovery of unusual massive shield volcanoes such as coronae and arachnoids

Arachnoid (astrogeology)

In astrogeology, an arachnoid is a large structure of unknown origin, and they have been found only on the surface of the planet Venus. Arachnoids get their name from their resemblance to spider webs. They appear as concentric ovals surrounded by a complex network of fractures, and can span 200...

. Venus had no evidence of plate tectonics, unless the northern third of the planet happened to be a single plate. The altimetry data obtained by the Venera missions had a resolution four times better than Pioneers.

Magellan

On August 10, 1990, the US Magellan

Magellan probe

The Magellan spacecraft, also referred to as the Venus Radar Mapper, was a 1,035-kilogram robotic space probe launched by NASA on May 4, 1989, to map the surface of Venus using Synthetic Aperture Radar and measure the planetary gravity...

probe, named after the explorer Ferdinand Magellan

Ferdinand Magellan

Ferdinand Magellan was a Portuguese explorer. He was born in Sabrosa, in northern Portugal, and served King Charles I of Spain in search of a westward route to the "Spice Islands" ....

, arrived at its orbit around the planet and started a mission of detailed radar

Radar

mapping at a frequency of 2.38 GHz. Whereas previous probes had created low-resolution radar maps of continent-sized formations, Magellan mapped 98% of the surface with a resolution of approximately 100 m. The resulting maps were comparable to visible-light photographs of other planets, and are still the most detailed in existence. Magellan greatly improved scientific understanding of the geology of Venus

Geology of Venus

Venus is a planet with striking surface characteristics. Most of what is known about its surface stems from radar observations, mainly images sent by the Magellan probe between August 16, 1990 and the end of its sixth orbital cycle in September 1994...

: the probe found no signs of plate tectonics

Plate tectonics

Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

, but the scarcity of impact craters suggested the surface was relatively young, and there were lava channel

Lava channel

A lava channel is a stream of fluid lava contained within marginal zones of static lava or levees. The initial channel may not contain levees per se, until the parental flow solidifies over what develops into the channel and creates simple levees. This initial levee allows for the building of a...

s thousands of kilometers long. After a four-year mission, Magellan, as planned, plunged into the atmosphere on October 11, 1994, and partly vaporized; some sections are thought to have hit the planet's surface.

Venus Express

is a mission by 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...

to study the atmosphere and surface characteristics of Venus from orbit. The design is based on ESA's 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 Rosetta

Rosetta

Rosetta is a port city on the Mediterranean coast of Egypt. It is located east of Alexandria, in Beheira governorate. It was founded around AD 800....

missions. The probe's main objective is the long-term observation of the Venusian atmosphere, which it is hoped will also contribute to an understanding of Earth's atmosphere and climate. It will also make global maps of Venusian surface temperatures, and attempt to observe signs of life on Earth from a distance.

Venus Express successfully assumed a polar orbit on April 11, 2006 and has been continuously sending back science data. The mission was originally planned to last for two Venusian years (about 500 Earth days), but has been extended to the end of 2012. Some of the first results emerging from Venus Express include evidence of past oceans, the discovery of a huge double atmospheric vortex

Polar vortex

A polar vortex is a persistent, large-scale cyclone located near one or both of a planet's geographical poles. On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere...

at the south pole, and the detection of hydroxyl

Hydroxyl

A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

in the atmosphere.

Akatsuki

Akatsuki was launched on May 20, 2010, by JAXA, and was planned to enter Venusian orbit in December 2010. However, the orbital insertion maneuver failed and the spacecraft was left in heliocentric orbit. Another attempt will be made when it again approaches the planet in 2016. The probe will image the surface in ultraviolet, infrared, microwaves, and radio, and look for evidence of lightning and volcanism on the planet.

Recent flybys

Several space probes en route to other destinations have used flybys of Venus to increase their speed via the gravitational slingshot

Gravitational slingshot

In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense...

method. These include the Galileo

Galileo spacecraft

Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission...

mission to 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,...

and the Cassini–Huygens mission to Saturn

Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

(two flybys). Rather curiously, during Cassinis examination of the radio frequency

Radio frequency

Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

emissions of Venus with its radio and plasma wave science instrument during both the 1998 and 1999 flybys, it reported no high-frequency radio waves (0.125 to 16 MHz), which are commonly associated with lightning. This was in direct opposition to the findings of the Soviet Venera missions 20 years earlier. It was postulated that perhaps if Venus did have lightning, it might be some type of low-frequency electrical activity, because radio signals cannot penetrate the ionosphere at frequencies below about 1 megahertz. At the University of Iowa, Donald Gurnett's examination of Venus's radio emissions by the Galileo spacecraft during its flyby in 1990 were interpreted at the time to be indicative of lightning. However the Galileo probe was over 60 times further from Venus than Cassini was during its flyby, making its observations substantially less significant. The mystery as to whether or not Venus does in fact have lightning in its atmosphere was not solved until 2007, when the scientific journal Nature

Nature (journal)

Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

published a series of papers giving the initial findings of Venus Express

Venus Express

. It confirmed the presence of lightning on Venus and that it is more common on Venus than it is on Earth.

MESSENGER

MESSENGER

The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...

passed by Venus twice on its way to Mercury. The first time, it flew by on October 24, 2006, passing 3000 km from Venus

Venus

. As 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...

was on the other side of 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...

, no data was recorded. The second flyby was on July 6, 2007, where the spacecraft passed only 325 km from the cloudtops.

Future missions

Future flybys en route to other destinations include the BepiColombo

BepiColombo

BepiColombo is a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency to the planet Mercury, due to launch in 2014. The mission is still in the planning stages so changes to the current description are likely over the next few years...

mission to Mercury, and the Solar Probe+ mission to the solar corona.

NASA has proposed the Venus In-Situ Explorer

Venus In-Situ Explorer

The Venus In-Situ Explorer is a mission that was proposed by the NASA planetary science Decadal Survey as a space probe designed to answer fundamental scientific questions by landing and performing experiments on Venus...

(VISE), to be launched in 2013. It would land and perform experiments on the surface of Venus, including taking a core sample

Core sample

A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. The hole made for the core sample is called the "core hole". A...

and measuring its composition. ESA has proposed the Venus Entry Probe

Venus Entry Probe

The Venus Entry Probe is a proposed European Space Agency space probe to Venus. The spacecraft is planned to be launched on a Soyuz-2/Fregat launch vehicle around 2013.-External links:*...

to be launched around the same time.

Also, the Venera-D

Venera-D

The Venera-D probe is a proposed Russian space probe to Venus, to be launched around 2016. Venera-D's prime purpose is to make remote-sensing observations around the planet Venus in a manner similar to that of the U.S. Magellan spacecraft in the 1990s, but with the use of more powerful radar....

spacecraft has been proposed by Roscosmos

Russian Federal Space Agency

The Russian Federal Space Agency , commonly called Roscosmos and abbreviated as FKA and RKA , is the government agency responsible for the Russian space science program and general aerospace research. It was previously the Russian Aviation and Space Agency .Headquarters of Roscosmos are located...

. It would be launched around 2016, and its prime purpose is to map Venus's surface using more powerful radar than Magellan. The mission would also include a lander capable of surviving for a long duration on the surface.

Proposals

To overcome the severely inhospitable surface conditions, a team led by Geoffrey Landis of NASA

NASA

's Glenn Research Center

Glenn Research Center

NASA John H. Glenn Research Center at Lewis Field is a NASA center, located within the cities of Brook Park, Cleveland and Fairview Park, Ohio between Cleveland Hopkins International Airport and the Cleveland Metroparks's Rocky River Reservation, and has other subsidiary facilities in Ohio...

in Ohio

Ohio

Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...

has proposed a Venus Rover mission that includes a tough surface rover in communication with a solar-powered aircraft. The aircraft would carry the mission's sensitive electronics in the relatively mild temperatures of Venus' upper atmosphere. Another more recent rover design proposal by Landis uses a Stirling cooler powered by a nuclear power source to keep an electronics package at a relatively comfortable 200°C (392°F)

Landis also makes a case for Venus as a target for human colonization

Colonization of Venus

The colonization of Venus has been a subject of much speculation and many works of science fiction since before the dawn of spaceflight, and is still much discussed...

. At 50 km above the surface, the temperature range is 0-50°C, the air pressure drops to 1 atmosphere, the gravity is 0.9 that of Earth, and the resources for life are plentiful.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.