Planetary science (or more rarely, planetology) is the scientific study of

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

s (including

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

), celestial bodies (such as

moons A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...

asteroids An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

comets A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

) and planetary systems (in particular those of the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

) and the processes of their formation. It studies objects ranging in size from micrometeoroids to

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

s, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly interdisciplinary field, which originally grew from

astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...

and Earth science, and now incorporates many disciplines, including planetary geology,

cosmochemistry Cosmochemistry (from Greek κόσμος ''kósmos'', "universe" and χημεία ''khemeía'') or chemical cosmology is the study of the chemical composition of matter in the universe and the processes that led to those compositions. This is done ...

, atmospheric science,

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...

, oceanography,

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...

, theoretical planetary science,

glaciology Glaciology (; ) is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice. Glaciology is an interdisciplinary Earth science that integrates geophysics, geology, physical geography, geomorphology, c ...

, and exoplanetology. Allied disciplines include space physics, when concerned with the effects of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

on the bodies of the Solar System, and astrobiology. There are interrelated observational and theoretical branches of planetary science. Observational research can involve combinations of space exploration, predominantly with robotic spacecraft missions using

remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Eart ...

, and comparative, experimental work in Earth-based

laboratories A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physici ...

. The theoretical component involves considerable computer simulation and

mathematical modelling A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, ...

. 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. Generally, planetary scientists study one of the

Earth sciences Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres ...

, astrophysics,

geophysics Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' so ...

, or

at the graduate level and concentrate their research in planetary science disciplines. There are several major conferences each year, and a wide range of

peer-reviewed journals An academic journal or scholarly journal is a periodical publication in which Scholarly method, scholarship relating to a particular list of academic disciplines, academic discipline is published. Academic journals serve as permanent and transpar ...

. Some planetary scientists work at private research centres and often initiate partnership research tasks.

History

The history of planetary science may be said to have begun with the Ancient Greek philosopher

Democritus Democritus (; el, Δημόκριτος, ''Dēmókritos'', meaning "chosen of the people"; – ) was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. No ...

, 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 Galileo, who discovered the four largest moons of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

, the mountains on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, and first observed the

rings of Saturn The rings of Saturn are the most extensive ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit around Saturn. The ring particles are made almost entir ...

, 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 A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...

construction and instrumental resolution gradually allowed increased identification of the atmospheric as well as surface details of the planets. The Moon was initially the most heavily studied, due to its proximity to the Earth, as it always exhibited elaborate features on its surface, and the technological improvements gradually produced more detailed lunar geological knowledge. In this scientific process, the main instruments were astronomical

optical telescope An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through elect ...

s (and later

radio telescopes A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency p ...

) and finally robotic exploratory

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

, such as

space probes Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually conside ...

. 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 Exploration refers to the historical practice of discovering remote lands. It is studied by geographers and historians. Two major eras of exploration occurred in human history: one of convergence, and one of divergence. The first, covering most ...

the Solar System.

Disciplines

Planetary science studies observational and theoretical astronomy,

geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

(

astrogeology Planetary 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. Although the geo ...

), atmospheric science, and an emerging subspecialty in

planetary ocean Europa , or Jupiter II, is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 80 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered in 161 ...

s, called

planetary oceanography Planetary oceanography also called exo-oceanography is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry and planetary geology, it only began after the discovery of under ...

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 Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...

are determined, and the history of their formation and evolution can be understood. Theoretical planetary astronomy is concerned with dynamics: the application of the principles of

celestial mechanics Celestial mechanics is the branch of astronomy that deals with the motions of objects in outer space. Historically, celestial mechanics applies principles of physics (classical mechanics) to astronomical objects, such as stars and planets, to ...

to the Solar System and

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

ary systems. Observing

exoplanets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

and determining their physical properties, exoplanetology, is a major area of research besides Solar System studies. Every planet has its own branch. Planet: Subject: Named after (NB: these terms are rarely used) * Mercury: Hermology:

Hermes Hermes (; grc-gre, wikt:Ἑρμῆς, Ἑρμῆς) is an Olympian deity in ancient Greek religion and Greek mythology, mythology. Hermes is considered the herald of the gods. He is also considered the protector of human heralds, travelle ...

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

: Cytherology: Cytherea *

Geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

: Gaia *

Selenology The geology of the Moon (sometimes called selenology, although the latter term can refer more generally to " lunar science") is quite different from that of Earth. The Moon lacks a true atmosphere, which eliminates erosion due to weather. It does ...

Selene In ancient Greek mythology and religion, Selene (; grc-gre, Σελήνη , meaning "Moon"''A Greek–English Lexicon's.v. σελήνη) is the goddess and the personification of the Moon. Also known as Mene, she is traditionally the daughter of ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

: Areology: Ares *

Ceres Ceres most commonly refers to: * Ceres (dwarf planet), the largest asteroid * Ceres (mythology), the Roman goddess of agriculture Ceres may also refer to: Places Brazil * Ceres, Goiás, Brazil * Ceres Microregion, in north-central Goiás ...

: Demeterology: Demeter *

: Zenology:

Zeus Zeus or , , ; grc, Δῐός, ''Diós'', label= genitive Boeotian Aeolic and Laconian grc-dor, Δεύς, Deús ; grc, Δέος, ''Déos'', label= genitive el, Δίας, ''Días'' () is the sky and thunder god in ancient Greek reli ...

* Saturn: Kronology: Kronos *

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...

: Uranology:

* Neptune: Poseidology:

Poseidon Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ...

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...

: Hadeology: Hades * Eris: Eridology: Eris

Planetary geology

In planetary science, the term geology is used in its broadest sense, to mean the study of the surface and interior parts of planets and moons, from their core to their magnetosphere. The best known research topics of planetary geology deal with the planetary bodies in the near vicinity of the Earth: the

, and the two neighbouring planets:

and

. Of these, the Moon was studied first, using methods developed earlier on the Earth. Planetary geology focuses on the celestial objects that exhibit a solid surface or have significant solid physical states as part of their structure. Planetary geology applies

and

geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...

to planetary bodies.

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 the study of several classes of surface features: * Impact features ( multi-ringed basins, craters) * Volcanic and tectonic features (lava flows, fissures,

rille Rille (German for 'groove') is typically used to describe any of the long, narrow depressions in the surface of the Moon that resemble channels. The Latin term is ''rima'', plural ''rimae''. Typically, a rille can be several kilometers wi ...

s) * Glacial features * Aeolian features *

Space weathering Space weathering is the type of weathering that occurs to any object exposed to the harsh environment of outer space. Bodies without atmospheres (including the Moon, Mercury, the asteroids, comets, and most of the moons of other planets) take on ...

– erosional effects generated by the harsh environment of space (continuous micro meteorite bombardment, high-energy particle rain,

impact gardening Impact 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. Planetary bodies lacking a ...

). For example, the thin dust cover on the surface of the

lunar Lunar most commonly means "of or relating to the Moon". Lunar may also refer to: Arts and entertainment * ''Lunar'' (series), a series of video games * "Lunar" (song), by David Guetta * "Lunar", a song by Priestess from the 2009 album ''Prior t ...

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestr ...

is a result of micro meteorite 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 are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

and

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

, depending on the location within the Solar System. This category includes the study of paleohydrological features (paleochannels, paleolakes). The history of a planetary surface can be deciphered by mapping features from top to bottom according to their deposition sequence, as first determined on terrestrial strata by

Nicolas Steno Niels Steensen ( da, Niels Steensen; Latinized to ''Nicolaus Steno'' or ''Nicolaus Stenonius''; 1 January 1638 – 25 November 1686stratigraphic mapping prepared the

Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label= Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label ...

astronauts for the field geology they would encounter on their lunar missions. Overlapping sequences were identified on images taken by the

Lunar Orbiter program The Lunar Orbiter program was a series of five uncrewed 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 f ...

, and these were used to prepare a lunar

stratigraphic column A 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. A typical stratigraphic column shows a sequence of sedimentary rocks, with the oldest ...

and

geological map A geologic map or geological map is a special-purpose map made to show various geological features. Rock (geology), Rock units or stratum, geologic strata are shown by color or symbols. Bed (geology), Bedding planes and structural features such ...

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. Direct samples from the Moon, asteroids and

are present on Earth, removed from their parent bodies and delivered as meteorites. Some of these have suffered contamination from the oxidising effect of Earth's atmosphere and the infiltration of the

biosphere The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also ...

, but those meteorites collected in the last few decades from

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

are almost entirely pristine. The different types of meteorites that originate from the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, c ...

cover almost all parts of the structure of differentiated bodies: meteorites even exist that come from the core-mantle boundary ( pallasites). The combination of geochemistry and observational astronomy has also made it possible to trace the

HED meteorite HED meteorites are a clan (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 mag ...

s back to a specific asteroid in the main belt,

4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...

. The comparatively few known

Martian meteorites A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a perc ...

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 lithosphere. As of July 24, 2013 65 samples of Martian meteorites have been discovered on Earth. Many were found in either Antarctica or the Sahara Desert. During the Apollo era, in the Apollo program, 384 kilograms of

lunar sample Moon rock or lunar rock is rock originating from Earth's Moon. This includes lunar material collected during the course of human exploration of the Moon, and rock that has been ejected naturally from the Moon's surface and landed on Earth as ...

s were collected and transported to the Earth, and three

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nation ...

Luna Luna commonly refers to: * Earth's Moon, named "Luna" in Latin * Luna (goddess), the ancient Roman personification of the Moon Luna may also refer to: Places Philippines * Luna, Apayao * Luna, Isabela * Luna, La Union * Luna, San Jose Roma ...

robots also delivered

samples from the Moon. These samples provide the most comprehensive record of the composition of any Solar System body beside the Earth. The numbers of lunar meteorites are growing quickly in the last few years – as of April 2008 there are 54 meteorites that have been officially classified as lunar. Eleven of these are from the US Antarctic meteorite collection, 6 are from the Japanese Antarctic meteorite collection, and the other 37 are from hot desert localities in Africa, Australia, and the Middle East. The total mass of recognized lunar meteorites is close to 50 kg.

Geophysics and Space Physics

Space probes made it possible to collect data in 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 field In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...

s of the planets to be mapped. For example, in the 1970s, the gravity field disturbances above

lunar maria The lunar maria (; singular: mare ) are large, dark, basaltic plains on Earth's Moon, formed by ancient asteroid impacts on the far side on the Moon that triggered volcanic activity on the opposite (near) side. They were dubbed , Latin for 'seas' ...

were measured through lunar orbiters, which led to the discovery of concentrations of mass, mascons, beneath the Imbrium, Serenitatis, Crisium, Nectaris and Humorum basins. Magnetosphere rendition

If a planet's magnetic field is sufficiently strong, its interaction with the solar wind forms a magnetosphere around a planet. Early space probes discovered the gross dimensions of the terrestrial magnetic field, which extends about 10 Earth radii towards the Sun. The

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

, 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 belts. Planetary

includes, but is not limited to,

seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...

and tectonophysics, geophysical fluid dynamics, mineral physics, geodynamics, mathematical geophysics, and geophysical surveying. Planetary geodesy (also known as planetary geodetics) deals with the measurement and representation of the planets of the Solar System, their gravitational fields and geodynamic phenomena (polar motion in three-dimensional, time-varying space. The science of geodesy has elements of both astrophysics and planetary sciences. The Earth's figure, 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 Volcano, vulcanism, resisted by the Earth's gravity field. These principles can be applied to the Solid Earth, solid surface of Earth (orogeny; Few mountains are higher than , few deep sea trenches deeper than that because quite simply, a mountain as tall as, for example, , would develop so much pressure at its base, due to gravity, that the rock there would become plastic, and the mountain would slump back to a height of roughly 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 Mons, is high at its peak, a height that could not be maintained on Earth. The Earth geoid is essentially the figure of the Earth abstracted from its topographic features. Therefore, the Mars geoid (areoid is essentially the figure of Mars abstracted from its topographic features. Surveying and mapping are two important fields of application of geodesy.

Planetary Atmospheric science

The atmosphere is an important transitional zone between the solid planetary surface and the higher rarefied Ionisation, 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

planets, almost all of the terrestrial planets (Earth's atmosphere, Earth, Atmosphere of Venus, Venus, and Atmosphere of Mars, Mars) have significant atmospheres. Two moons have significant atmospheres: Saturn's moon Titan (moon), Titan and Neptune's moon Atmosphere of Triton, Triton. A tenuous atmosphere exists around Mercury. The effects of the Planet#Rotation, 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.

Planetary oceanography

Exoplanetology

Exoplanetology studies exoplanets, the planets existing outside our

. Until recently, the means of studying exoplanets have been extremely limited, but with the current rate of innovation in Scientific instrument, research technology, exoplanetology has become a rapidly developing :Astronomical sub-disciplines, subfield of astronomy.

Comparative planetary science

Planetary science frequently makes use of the method of comparison to give a greater understanding of the object of study. This can involve comparing the dense atmospheres of Earth and Saturn's moon Titan (moon), Titan, 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. The use of terrestrial analogues was first described by Gilbert (1886).

Professional activity

Journals

* ''Annual Review of Earth and Planetary Sciences'' * ''Earth and Planetary Science Letters'' * ''Earth, Moon, and Planets'' * ''Geochimica et Cosmochimica Acta'' * ''Icarus (journal), Icarus'' * ''Journal of Geophysical Research, Journal of Geophysical Research – Planets'' * ''Meteoritics and Planetary Science'' * ''Planetary and Space Science'' * ''The Planetary Science Journal''

Professional bodies

* Division for Planetary Sciences (DPS) of the American Astronomical Society * American Geophysical Union * Meteoritical Society * Europlanet

Major conferences

* Lunar and Planetary Science Conference (LPSC), organized by the Lunar and Planetary Institute in Houston. Held annually since 1970, occurs in March. * Division for Planetary Sciences (DPS) meeting held annually since 1970 at a different location each year, predominantly within the mainland US. Occurs around October. * American Geophysical Union (AGU) annual Fall meeting in December in San Francisco. * American Geophysical Union (AGU) Joint Assembly (co-sponsored with other societies) in April–May, in various locations around the world. * Meteoritical Society 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. 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. Alphabetical order is used.

National space agencies

* Canadian Space Agency (CSA). Annual budget CAD $488.7 million (2013–2014). * China National Space Administration (CNSA) (People's Republic of China). Budget $0.5–1.3 billion (est.). * CNES, Centre national d'études spatiales French National Centre of Space Research,Budget €1.920 billion (2012). * German Aerospace Center, Deutsches Zentrum für Luft- und Raumfahrt e.V., (German: abbreviated DLR), the German Aerospace Center. Budget $2 billion (2010). * European Space Agency (ESA). Budget $5.51 billion (2013). * Indian Space Research Organisation (ISRO), * Israel Space Agency (ISA), * Italian Space Agency Budget ~$1 billion (2010). * Japan Aerospace Exploration Agency (JAXA). Budget $2.15 billion (2012). * NASA: Considerable number of research groups, including the Jet Propulsion Laboratory, JPL, Goddard Space Flight Center, GSFC, NASA Ames Research Center, Ames. Budget $18.72 billion (2011). * National Space Organization (Taiwan). * Russian Federal Space Agency Budget $5.61 billion (2013). * UK Space Agency (UKSA).

Other institutions

* Arctic Planetary Science Institute
Arizona State University

School of Earth and Space Exploration
* The Australian National University'
Planetary Science Institute
* Brown University]
Planetary Geosciences Group
* Caltech'
Division of Geological and Planetary Sciences
an
Planetary Sciences subdivision
* Cornell University's
Space and Planetary Science
* Curtin University'
School of Earth and Planetary Sciences
* Florida Institute of Technology'
Department of Physics and Space Sciences
* Johns Hopkins University, Johns Hopkins University's]
Applied Physics Laboratory
* Lunar and Planetary Institute * Max Planck Institute for Solar System Research'
Department Planets and Comets
* Massachusetts Institute of Technology, MIT]
Dept. of Earth, Atmospheric and Planetary Sciences
* Open University]
Planetary and Space Sciences Research Institute
* Planetary Science Institute * Stony Brook University'
Geosciences Department
and soon to open Center for Planetary Exploration * University College London, UCL/Birkbeck, University of London, Birkbeck'
Centre for Planetary Sciences
* University of Arizona'
Lunar and Planetary Lab
* University of Arkansas'
Center for Space and Planetary Sciences
* University of California Los Angeles'
Department of Earth, Planetary, and Space Sciences
* University of California Santa Cruz'
Department of Earth & Planetary Sciences
* University of Hawaii'
Hawaii Institute of Geophysics and Planetology
* University of Copenhagen's Center for Planetary Research (Copenhagen University), Center for Planetary Research * University of Central Florida]
Planetary Sciences Group
* University of British Columbia]
Department of Earth, Ocean and Atmospheric Sciences
* University of Western Ontario's CPSX, Centre for Planetary Science and Exploration * University of Tennessee]
Department of Earth and Planetary Sciences
* University of Colorado's Department o
Astrophysical and Planetary Sciences

Washington University in St. Louis

Department of Earth and Planetary Sciences
* INAF �
Istituto di Astrofisica e Planetologia Spaziali
(:it:Istituto di Astrofisica e Planetologia Spaziali, it)

Basic concepts

* Asteroid * Celestial mechanics * Comet * Dwarf planet * Extrasolar planet * Gas giant * Icy moon * Kuiper belt * Magnetosphere * Minor planet * Planet * Planetary differentiation * Planetary system * Definition of a planet * Space weather * Synestia * Terrestrial planet

References

External links

Planetary Science Research Discoveries
(articles)
The Planetary Society
(world's largest space-interest group: see also their active new
blog

Planetary Exploration Newsletter
(PSI-published professional newsletter, weekly distribution)
Women in Planetary Science
(professional networking and news) {{Authority control Planetary science, Space science Astronomical sub-disciplines