Planetary science is the scientific study of
planetA 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,...
s (including
EarthEarth 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...
),
moonsA natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
, and
planetary systemA planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
s, in particular those of the
Solar SystemThe 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...
and the processes that form them. It studies objects ranging in size from
micrometeoroidA micrometeoroid is a tiny meteoroid; a small particle of rock in space, usually weighing less than a gram. A micrometeor or micrometeorite is such a particle that enters the Earth's atmosphere or falls to Earth.-Scientific interest:...
s to
gas giantA gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
s, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly
interdisciplinaryInterdisciplinarity involves the combining of two or more academic fields into one single discipline. An interdisciplinary field crosses traditional boundaries between academic disciplines or schools of thought, as new needs and professions have emerged....
field, originally growing from
astronomyAstronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
and
earth scienceEarth science is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth sciences...
, but which now incorporates many disciplines, including planetary astronomy,
planetary geologyPlanetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites...
(together with
geochemistryThe field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
and
geophysicsGeophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
), atmospheric science,
oceanographyOceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
,
hydrologyHydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...
, theoretical planetary science,
glaciologyGlaciology Glaciology Glaciology (from Middle French dialect (Franco-Provençal): glace, "ice"; or Latin: glacies, "frost, ice"; and Greek: λόγος, logos, "speech" lit...
, and the study of extrasolar planets. Allied disciplines include
space physicsSpace physics, also known as space plasma physics, is the study of plasmas as they occur naturally in the universe. As such, it encompasses a far-ranging number of topics, including the sun, solar wind, planetary magnetospheres and ionospheres, auroras, cosmic rays, and synchrotron radiation...
, when concerned with the effects of the
SunThe 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...
on the bodies of the Solar System, and
astrobiologyAstrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This interdisciplinary field encompasses the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry,...
.
There are interrelated observational and theoretical branches of planetary science. Observational research can involve a combination of
space explorationSpace 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....
, predominantly with
robotic spacecraftA 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...
missions using
remote sensingRemote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth by means of propagated signals Remote sensing...
, and comparative, experimental work in Earth-based laboratories. The theoretical component involves considerable
computer simulationA computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
and mathematical modelling.
Planetary scientists are generally located in the astronomy and physics or earth sciences departments of universities or research centres, though there are several purely planetary science institutes worldwide. There are several major conferences each year, and a wide range of
peer-reviewed journalsAn academic journal is a peer-reviewed periodical in which scholarship relating to a particular academic discipline is published. Academic journals serve as forums for the introduction and presentation for scrutiny of new research, and the critique of existing research...
.
History
The history of planetary science may be said to have begun with the Ancient Greek philosopher
DemocritusDemocritus was an Ancient Greek philosopher born in Abdera, Thrace, Greece. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated an atomic theory for the cosmos....
, who is reported by Hippolytus as saying
"The ordered worlds are boundless and differ in size, and that in some there is neither sun nor moon, but that in others, both are greater than with us, and yet with others more in number. And that the intervals between the ordered worlds are unequal, here more and there less, and that some increase, others flourish and others decay, and here they come into being and there they are eclipsed. But that they are destroyed by colliding with one another. And that some ordered worlds are bare of animals and plants and all water."
In more modern times, planetary science began in astronomy, from studies of the unresolved planets. In this sense, the original planetary astronomer would be
GalileoGalileo 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 discovered the four largest moons of
JupiterJupiter 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,...
, the mountains on the
MoonThe 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 first observed the
rings of SaturnThe rings of Saturn are the most extensive planetary ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometres to metres, that form clumps that in turn orbit about Saturn...
, all objects of intense later study. Galileo's study of the lunar mountains in 1609 also began the study of extraterrestrial landscapes: his observation "that the Moon certainly does not possess a smooth and polished surface" suggested that it and other worlds might appear "just like the face of the Earth itself".
Advances in telescope construction and instrumental resolution gradually allowed increased identification of the atmospheric and surface details of the planets. The Moon was initially the most heavily studied, as it always exhibited details on its surface, due to its proximity to the Earth, and the technological improvements gradually produced more detailed lunar geological knowledge. In this scientific process, the main instruments were astronomical
optical telescopeAn optical telescope is a telescope which is used to gather and focus light mainly from the visible part of the electromagnetic spectrum for directly viewing a magnified image for making a photograph, or collecting data through electronic image sensors....
s (and later radio telescopes) and finally robotic exploratory
spacecraftA 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...
.
The Solar System has now been relatively well-studied, and a good overall understanding of the formation and evolution of this planetary system exists. However, there are large numbers of unsolved questions, and the rate of new discoveries is very high, partly due to the large number of interplanetary spacecraft currently exploring the Solar System.
Planetary astronomy
This is both an observational and a theoretical science. Observational researchers are predominantly concerned with the study of the small bodies of the solar system: those that are observed by telescopes, both optical and radio, so that characteristics of these bodies such as shape, spin, surface materials and weathering are determined, and the history of their formation and evolution can be understood.
Theoretical planetary astronomy is concerned with
dynamicsIn classical mechanics, analytical dynamics, or more briefly dynamics, is concerned about the relationship between motion of bodies and its causes, namely the forces acting on the bodies and the properties of the bodies...
: the application of the principles of
celestial mechanicsCelestial mechanics is the branch of astronomy that deals with the motions of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics is a subfield which focuses on...
to the Solar System and extrasolar
planetary systemA planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
s.
Planetary geology
The best known research topics of planetary geology deal with the planetary bodies in the near vicinity of the Earth: the
MoonThe 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 two neighbouring planets:
VenusVenus 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...
and
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. Of these, the Moon was studied first, using methods developed earlier on the Earth.
Geomorphology
Geomorphology studies the features on planetary surfaces and reconstructs the history of their formation, inferring the physical processes that acted on the surface. Planetary geomorphology includes study of several classes of surface feature:
- Impact features (multi-ringed basins, craters)
- Volcanic and tectonic features (lava flows, fissures, rille
Rille is typically used to describe any of the long, narrow depressions in the lunar surface that resemble channels. Typically a rille can be up to several kilometers wide and hundreds of kilometers in length...
s)
- Space weathering
Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment. Airless bodies incur many weathering processes:* collisions of galactic cosmic rays and solar cosmic rays,* irradiation, implantation, and sputtering from solar wind...
- erosional effects generated by the harsh environment of space (continuous micrometeorite bombardment, high-energy particle rain, impact gardeningImpact gardening is the process by which impact events stir the outermost crusts of moons and other celestial objects with no atmospheres. In the particular case of the Moon, this is more often known as lunar gardening...
). For example, the thin dust cover on the surface of the lunarThe 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...
regolithRegolith 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:...
is a result of micrometeorite bombardment.
- Hydrological features: the liquid involved can range from water to hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
and ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
, depending on the location within the Solar System.
The history of a planetary surface can be deciphered by mapping features from top to bottom according to their
deposition sequenceThe law of superposition is a key axiom based on observations of natural history that is a foundational principle of sedimentary stratigraphy and so of other geology dependent natural sciences:...
, as first determined on terrestrial
strataIn geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
by
Nicolas StenoNicolas Steno |Latinized]] to Nicolaus Steno -gen. Nicolai Stenonis-, Italian Niccolo' Stenone) was a Danish pioneer in both anatomy and geology. Already in 1659 he decided not to accept anything simply written in a book, instead resolving to do research himself. He is considered the father of...
. For example,
stratigraphic mappingStratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
prepared the Apollo astronauts for the field geology they would encounter on their lunar missions. Overlapping sequences were identified on images taken by the
Lunar Orbiter programThe Lunar Orbiter program was a series of five unmanned lunar orbiter missions launched by the United States from 1966 through 1967. Intended to help select Apollo landing sites by mapping the Moon's surface, they provided the first photographs from lunar orbit.All five missions were successful,...
, and these were used to prepare a lunar
stratigraphic columnA stratigraphic column is a representation used in geology and its subfield of stratigraphy to describe the vertical location of rock units in a particular area....
and
geological mapA geologic map or geological map is a special-purpose map made to show geological features. Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface...
of the Moon.
Cosmochemistry, geochemistry and petrology
One of the main problems when generating hypotheses on the formation and evolution of objects in the Solar System is the lack of samples that can be analysed in the laboratory, where a large suite of tools are available and the full body of knowledge derived from terrestrial geology can be brought to bear. Fortunately, direct samples from the Moon,
asteroidAsteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s and
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
are present on Earth, removed from their parent bodies and delivered as
meteoriteA 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...
s. Some of these have suffered contamination from the oxidising effect of Earth's atmosphere and the infiltration of the
biosphereThe biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...
, but those meteorites collected in the last few decades from
Antarctica are almost entirely pristine.
The different types of meteorite that originate from the
asteroid beltThe 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...
cover almost all parts of the structure of
differentiatedIn planetary science, planetary differentiation is the process of separating out different constituents of a planetary body as a consequence of their physical or chemical behaviour, where the body develops into compositionally distinct layers; the denser materials of a planet sink to the center,...
bodies: meteorites even exist that come from the core-mantle boundary (
pallasiteA pallasite is a type of stony–iron meteorite.-Structure and composition:It consists of cm-sized olivine crystals of peridot quality in an iron-nickel matrix. Coarser metal areas develop Widmanstätten patterns upon etching...
s). The combination of geochemistry and observational astronomy has also made it possible to trace the
HED meteoriteHED meteorites are a subgroup of achondrite meteorites. HED stands for "Howardite–Eucrite–Diogenite".These achondrites came from a differentiated parent body and experienced extensive igneous processing not much different from the magmatic rocks found on Earth and for this reason they closely...
s back to a specific asteroid in the main belt,
4 VestaVesta, 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....
.
The comparatively few known Martian meteorites have provided insight into the geochemical composition of the Martian crust, although the unavoidable lack of information about their points of origin on the diverse Martian surface has meant that they do not provide more detailed constraints on theories of the evolution of the Martian
lithosphereThe lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
. About 50 Martian meteorites have been identified, as of 2008.
During the Apollo era, in the Apollo program, 384 kilograms of lunar samples were collected and transported to the Earth, and 3 Soviet
LunaThe Luna programme , occasionally called Lunik or Lunnik, was a series of robotic spacecraft missions sent to the Moon by the Soviet Union between 1959 and 1976. Fifteen were successful, each designed as either an orbiter or lander, and accomplished many firsts in space exploration...
robots also delivered
regolithRegolith 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:...
samples from the Moon. These samples provide the most comprehensive record of the composition of any Solar System body beside the Earth. About 100 paired lunar meteorites are also known, as of 2008.
Geophysics
Space probes made it possible to collect data not only the visible light region, but in other areas of the electromagnetic spectrum. The planets can be characterized by their force fields: gravity and their magnetic fields, which are studied through geophysics and space physics.
Measuring the changes in acceleration experienced by spacecraft as they orbit has allowed fine details of the gravity fields of the planets to be mapped. For example, in the 1970s, the gravity field disturbances above lunar maria were measured through lunar orbiters, which lead to the discovery of concentrations of mass,
masconsIn astronomy or astrophysics mass concentration or mascon is a region of a planet or moon's crust that contains a large positive gravitational anomaly. In general, the word "mascon" can be used as a noun to describe an excess distribution of mass on or beneath the surface of a planet , such as Hawaii...
, beneath the Imbrium, Serenitatis, Crisium, Nectaris and Humorum basins.
If a planet's
magnetic fieldA 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;...
is sufficiently strong, its interaction with the solar wind forms a
magnetosphereA 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,...
around a planet. Early space probes discovered the gross dimensions of the terrestrial magnetic field, which extends about 10 Earth radiii towards the Sun. The
solar windThe 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...
, a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail, hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles, the
Van Allen radiation beltThe Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...
s.
Geophysics includes
seismologySeismology 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,...
and
tectonophysicsTectonophysics, a branch of geophysics, is the study of the physical processes that underlie tectonic deformation. The field encompasses the spatial patterns of stress, strain, and differing rheologies in the lithosphere and asthenosphere of the Earth; and the relationships between these patterns...
,
geophysical fluid dynamicsGeophysical fluid dynamics is the study of naturally occurring, large-scale flows on Earth and other planets. It is applied to the motion of fluids in the ocean and outer core, and to gases in the atmosphere of Earth and other planets...
,
mineral physicsMineral physics is the science of materials that compose the interior of planets, particularly the Earth. It overlaps with petrophysics, which focuses on whole-rock properties...
,
geodynamicsGeodynamics is a subfield of geophysics dealing with dynamics of the Earth. It applies physics, chemistry and mathematics to the understanding of how mantle convection leads to plate tectonics and geologic phenomena such as seafloor spreading, mountain building, volcanoes, earthquakes, faulting and...
,
mathematical geophysicsMathematical geophysics is concerned with developing mathematical methods for use in geophysics. As such, it has application in many fields in geophysics, particularly geodynamics and seismology.- Geophysical fluid dynamics :...
, and geophysical surveying.
GeodesyGeodesy , also named geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal...
, also called
geodetics, deals with the measurement and representation of the planets of the Solar System, their
gravitationGravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
al fields and geodynamic phenomena (
polar motionPolar motion of the earth is the movement of Earth's rotational axis across its surface. This is measured with respect to a reference frame in which the solid Earth is fixed...
in three-dimensional, time-varying space. The science of geodesy has elements of both astrophysics and planetary sciences. The shape of the Earth is to a large extent the result of its rotation, which causes its equatorial bulge, and the competition of geologic processes such as the collision of plates and of
vulcanism2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
, resisted by the Earth's gravity field. These principles can be applied to the solid surface of Earth (
orogenyOrogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
; Few mountains are higher than 10 km (6 mi), few deep sea trenches deeper than that because quite simply, a mountain as tall as, for example, 15 km (9 mi), would develop so much
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
at its base, due to gravity, that the rock there would become
plasticA plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
, and the mountain would slump back to a height of roughly 10 km (6 mi) in a geologically insignificant time. Some or all of these geologic principles can be applied to other planets besides Earth. For instance on Mars, whose surface gravity is much less, the largest volcano,
Olympus MonsOlympus 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...
, is 27 km (17 mi) high at its peak, a height that could not be maintained on Earth. The Earth
geoidThe 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...
is essentially the figure of the Earth abstracted from its topographic features. Therefore the Mars geoid is essentially the figure of Mars abstracted from its topographic features.
SurveyingSee Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...
and
mapA map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....
ping are two important fields of application of geodesy.
Atmospheric science
The
atmosphereAn 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...
is an important transitional zone between the solid planetary surface and the higher rarefied ionizing and radiation belts. Not all planets have atmospheres: their existence depends on the mass of the planet, and the planet's distance from the Sun — too distant and frozen atmospheres occur. Besides the four
gas giantA gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
planets, almost all of the terrestrial planets (
EarthThe atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
,
VenusThe 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...
, and
MarsThe atmosphere of Mars is relatively thin and is composed mostly of carbon dioxide . There has been interest in studying its composition since the detection of trace amounts of methane, which may indicate the presence of life on Mars, but may also be produced by a geochemical process, volcanic or...
) have significant atmospheres. Two moons have significant atmospheres:
SaturnSaturn 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,...
's moon
TitanTitan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
and
NeptuneNeptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
's moon
TritonThe atmosphere of Triton extends 800 kilometers above Triton's surface. The atmosphere mainly is composed of nitrogen, similar to Titan's atmosphere and Earth's atmosphere. The surface pressure is only 14 microbars, which is 1/70,000th of the surface pressure on Earth. Originally, it was thought...
. A tenuous atmosphere exists around
MercuryMercury 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...
.
The effects of the rotation rate of a planet about its axis can be seen in atmospheric streams and currents. Seen from space, these features show as bands and eddies in the cloud system, and are particularly visible on Jupiter and Saturn.
Comparative planetary science
Planetary science frequently makes use of the method of comparison to give greater understanding of the object of study. This can involve comparing the dense atmospheres of Earth and Saturn's moon
TitanTitan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
, the evolution of outer Solar System objects at different distances from the Sun, or the geomorphology of the surfaces of the terrestrial planets, to give only a few examples.
The main comparison that can be made is to features on the Earth, as it is much more accessible and allows a much greater range of measurements to be made. Earth analogue studies are particularly common in planetary geology, geomorphology, and also in atmospheric science.
Journals
- Icarus
Icarus is a premier scientific journal dedicated to the field of planetary science. It is published under the auspices of the American Astronomical Society's Division for Planetary Sciences . The longtime publisher was Academic Press, which is now part of Elsevier...
- Journal of Geophysical Research—Planets
The Journal of Geophysical Research is a peer-reviewed scientific journal published by the American Geophysical Union 80 times per year. It contains original research on the physical, chemical, and biological processes that contribute to the understanding of the Earth, Sun, and solar system...
- Earth and Planetary Science Letters
- Geochimica et Cosmochimica Acta
Geochimica et Cosmochimica Acta or GCA, established in 1950, is a semi-monthly, peer reviewed, scientific journal published by Elsevier. It is sponsored by the Geochemical Society and the Meteoritical Society. The current Executive editor, since the year 2000, is Frank Podosek...
- Meteoritics and Planetary Science
- Planetary and Space Science
Journal Citation Reports rates this journal with an impact factor of 2.344 for 2011, 2.067 for 2009 and 2.506 for 2008....
Professional bodies
- Division for Planetary Sciences
The Division for Planetary Sciences is a division within the American Astronomical Society devoted to solar system research. It was founded in 1968. The first organizing committee members were: Edward Anders, L. Branscomb, J. W. Chamberlain, R. Goody, J. S. Hall, A. Kliore, M. B. Elroy, Tobias...
(DPS) of the American Astronomical SocietyThe American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC...
- Meteoritical Society
The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials that further our understanding of the origin and history of the solar system.The...
- Europlanet
Europlanet is a network linking planetary scientists from across Europe. The aim of Europlanet is to promote collaboration and communication between partner institutions and to support missions to explore our Solar System....
Major conferences
- Lunar and Planetary Science Conference
The Lunar and Planetary Science Conference , jointly sponsored by the Lunar and Planetary Institute and NASA Johnson Space Center , brings together international specialists in petrology, geochemistry, geophysics, geology and astronomy to present the latest results of research in planetary science...
(LPSC), organized by the Lunar and Planetary InstituteThe Lunar and Planetary Institute is a scientific research institute dedicated to study of the solar system, its formation, evolution, and current state. The Institute is part of the Universities Space Research Association and is supported by the Science Mission Directorate of the National...
in Houston. Held annually since 1970, occurs in March.
- American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
(AGU) Joint Assembly (co-sponsored with other societies) in April-May, in various locations around the world.
- Meteoritical Society
The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials that further our understanding of the origin and history of the solar system.The...
annual meeting, held during the Northern Hemisphere summer, generally alternating between North America and Europe.
- European Planetary Science Congress (EPSC), held annually around September at a location within Europe.
- DPS
-Schools:* Dearborn Public Schools, the public school district in Dearborn, Michigan, United States* Delhi Public Schools, a large number of private schools mostly in India and few in other countries run by the Delhi Public School Society...
annual meeting, held around October at a different location each year, predominantly within the mainland US.
- AGU
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
annual meeting in December in San Francisco.
Smaller workshops and conferences on particular fields occur worldwide throughout the year.
Major institutions
This non-exhaustive list includes those institutions and universities with major groups of people working in planetary science.
- 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...
- 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...
: Considerable number of research groups, including the JPLJet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
, GSFCThe Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
, AmesThe Ames Research Center , is one of the United States of America's National Aeronautics and Space Administration 10 major field centers.The centre is located in Moffett Field in California's Silicon Valley, near the high-tech companies, entrepreneurial ventures, universities, and other...
- MIT
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
Dept. of Earth, Atmospheric and Planetary Sciences
- Lunar and Planetary Institute
The Lunar and Planetary Institute is a scientific research institute dedicated to study of the solar system, its formation, evolution, and current state. The Institute is part of the Universities Space Research Association and is supported by the Science Mission Directorate of the National...
- University of Arizona
The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...
's Lunar and Planetary Lab
- University of California Santa Cruz's Department of Earth & Planetary Sciences
- UCLA Dept. of Earth and Space Sciences
- Caltech's Division of Geological and Planetary Sciences
- Brown University
Brown University is a private, Ivy League university located in Providence, Rhode Island, United States. Founded in 1764 prior to American independence from the British Empire as the College in the English Colony of Rhode Island and Providence Plantations early in the reign of King George III ,...
Planetary Geosciences Group
- University of Hawaii
The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...
's Hawaii Institute of Geophysics and Planetology
- University of Copenhagen
The University of Copenhagen is the oldest and largest university and research institution in Denmark. Founded in 1479, it has more than 37,000 students, the majority of whom are female , and more than 7,000 employees. The university has several campuses located in and around Copenhagen, with the...
's Center for Planetary Research
- University of Central Florida
The University of Central Florida, commonly referred to as UCF, is a metropolitan public research university located in Orlando, Florida, United States...
Planetary Sciences Group
- University of British Columbia
The University of British Columbia is a public research university. UBC’s two main campuses are situated in Vancouver and in Kelowna in the Okanagan Valley...
Institute for Planetary Science
- University of Western Ontario
The University of Western Ontario is a public research university located in London, Ontario, Canada. The university's main campus covers of land, with the Thames River cutting through the eastern portion of the main campus. Western administers its programs through 12 different faculties and...
- CPSXThe Centre for Planetary Science and Exploration is an academic unit operating at the University of Western Ontario . Founded in 2007, dedicated in 2008 alongside the Canadian Lunar Research Network, it is the largest single group of planetary scientists working at an educational institution...
- Open University
The Open University is a distance learning and research university founded by Royal Charter in the United Kingdom...
Planetary and Space Sciences Research Institute
- Planetary Science Institute
The Planetary Science Institute is a research institute based in Tucson, Arizona, focusing on planetary science.Founded in 1972 on a non-profit basis, it is involved in many NASA missions, the study of Mars, asteroids, comets, interplanetary dust, the formation of the Solar System, extrasolar...
- The Australian National University
The Australian National University is a teaching and research university located in the Australian capital, Canberra.As of 2009, the ANU employs 3,945 administrative staff who teach approximately 10,000 undergraduates, and 7,500 postgraduate students...
's Planetary Science Institute
- University of Tennessee
The University of Tennessee is a public land-grant university headquartered at Knoxville, Tennessee, United States...
Planetary Geoscience
- University of Colorado
The University of Colorado system is a system of public universities in Colorado consisting of three universities in four campuses: University of Colorado Boulder, University of Colorado Colorado Springs, and University of Colorado Denver in downtown Denver and at the Anschutz Medical Campus in...
's Department of Astrophysical and Planetary Sciences
- Johns Hopkins University Applied Physics Laboratory http://www.jhuapl.edu
Basic concepts
- 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...
- Celestial mechanics
Celestial mechanics is the branch of astronomy that deals with the motions of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics is a subfield which focuses on...
- 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...
- 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...
- Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
- Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
- Icy moon
Icy moons are believed to be a common class of natural satellites or planetoids with surfaces composed mostly of ice. An icy moon may harbor an ocean underneath the surface, and possibly include a rocky core of silicate or metallic rocks. It is thought that they may be composed of ice II...
- Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
- 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,...
- Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
- 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,...
- Planetary differentiation
In planetary science, planetary differentiation is the process of separating out different constituents of a planetary body as a consequence of their physical or chemical behaviour, where the body develops into compositionally distinct layers; the denser materials of a planet sink to the center,...
- Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
- Definition of a planet
- Space weather
Space weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...
- 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...
Further reading
- Carr, Michael H., Saunders, R. S., Strom, R. G., Wilhelms, D. E. 1984. The Geology of the Terrestrial Planets. NASA.
- Morrison, David. 1994. Exploring Planetary Worlds. W.H. Freeman. ISBN 0716750430
See also
- Theoretical planetology
Theoretical planetology, also known as theoretical planetary science is a branch of planetary sciences that developed in the 20th century.- Nature of the work :...
- Timeline of Solar System exploration
This is a timeline of Solar System exploration ordered by date of spacecraft launch. It includes:*All spacecraft that have left Earth orbit for the purposes of Solar System exploration , including lunar probes....
- Selenography
Selenography is the study of the surface and physical features of the Moon. Historically, the principal concern of selenographists was the mapping and naming of the lunar maria, craters, mountain ranges, and other various features...
- study of the surface and physical features of the Moon
External links