Planetary geology

Planetary geologist and NASA astronaut Harrison "Jack" Schmitt collecting lunar samples during the Apollo 17 mission in early-December 1972
Surface of Mars in a false-color photograph by the Viking 2 lander, December 9, 1977
European Space Agency Huygens in situ image from Titan's surface—the only image from the surface of a body farther away than Mars
Same image with contrast enhanced

Planetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of celestial bodies such as planets and their moons, asteroids, comets, and meteorites. Although the geo- prefix typically indicates topics of or relating to Earth, planetary geology is named as such for historical and convenience reasons; due to the types of investigations involved, it is closely linked with Earth-based geology. These investigations are centered around the composition, structure, processes, and history of a celestial body.

Planetary geology includes such topics as determining the properties and processes of the internal structure of the terrestrial planets, and also looks at planetary volcanism and surface processes such as impact craters, fluvial and aeolian processes. The structures and compositions of the giant planets and their moons are also examined, as is the make-up of the minor bodies of the Solar System, such as asteroids, the Kuiper belt, and comets. Planetary geology largely applies concepts within the geosciences to planetary bodies in the broadest sense, includes applications derived from fields in the geological sciences, such as geophysics and geochemistry.

History of planetary geology

Eugene Merle Shoemaker is credited with bringing geologic principles to planetary mapping and creating the branch of planetary science in the early 1960s, the Astrogeology Research Program, within the United States Geological Survey. He made important contributions to the field and the study of impact craters, selenography (study of the Moon), asteroids, and comets.

Today, many institutions are concerned with the study and communication of planetary sciences and planetary geology. The Visitor Center at Barringer Meteor Crater near Winslow, Arizona includes a museum of planetary geology.[citation needed] The Geological Society of America's Planetary Geology Division has been growing and thriving since May 1981 and has two mottos: "One planet just isn't enough!" and ""The GSA Division with the biggest field area!"[citation needed]

Major centers for planetary science research include the Lunar and Planetary Institute, Applied Physics Laboratory, Planetary Science Institute, Jet Propulsion Laboratory, Southwest Research Institute, and Johnson Space Center. Additionally, several universities conduct extensive planetary science research, including Montana State University, Brown University, the University of Arizona, California Institute of Technology, University of Colorado, Western Michigan University, Massachusetts Institute of Technology, and Washington University in St. Louis. Planetary geologists usually study either geology, astronomy, planetary science, geophysics, or one of the earth sciences at the graduate level.


Several tools, including common archaeological tools such as hammers, shovels, brushes, etc. are often used by planetary geologists. Along with these common tools, new advanced technologies are used by planetary geologists. Scientists use maps, images, telescopes on Earth, and orbiting telescopes (such as the Hubble Space Telescope). The maps and images are stored in the NASA Planetary Data System where tools such as the Planetary Image Atlas help to search for certain items such as geological features including mountains, ravines, and craters.

Features and terms

Planetary geology uses a wide variety of standardized descriptor names for features. All planetary feature names recognized by the International Astronomical Union (IAU) combine one of these names with a possibly unique identifying name. The conventions which decide the more precise name are dependent on which planetary body the feature is on, but the standard descriptors are in general common to all astronomical planetary bodies. Some names have a long history of historical usage, but new must be recognized by the IAU Working Group for Planetary System Nomenclature as features are mapped and described by new planetary missions. This means that in some cases, names may change as new imagery becomes available, or in other cases widely adopted informal names changed in line with the rules. The standard names are chosen to consciously avoid interpreting the underlying cause of the feature, but rather to describe only its appearance.

Feature Pronunciation Description Designation
Albedo feature /ælˈbiːdoʊ/ An area which shows a contrast in brightness or darkness (albedo) with adjacent areas. This term is implicit. AL
Arcus, arcūs /ˈɑːrkəs/ Arc: curved feature AR
Astrum, astra /ˈæstrəm/, /ˈæstrə/ Radial-patterned features on Venus AS
Catena, catenae /kəˈtiːnə/, /kəˈtiːni/ A chain of craters e.g. Enki Catena. CA
Cavus, cavi /ˈkeɪvəs/, /ˈkeɪvaɪ/ Hollows, irregular steep-sided depressions usually in arrays or clusters CB
Chaos /ˈkeɪɒs/ A distinctive area of broken or jumbled terrain e.g. Iani Chaos. CH
Chasma, chasmata /ˈkæzmə/, /ˈkæzmətə/ Deep, elongated, steep-sided depression e.g. Eos Chasma. CM
Colles /ˈkɒliːz/ A collection of small hills or knobs. CO
Corona, coronae /kɒˈroʊnə/, /kɒˈroʊni/ An oval feature. Used only on Venus and Miranda. CR
Crater, craters /ˈkreɪtər/ A circular depression likely created by impact event. This term is implicit. AA
Dorsum, dorsa /ˈdɔːrsəm/, /ˈdɔːrsə/ Ridge, sometimes called a wrinkle ridge e.g. Dorsum Buckland. DO
Eruptive center An active volcano on Io. This term is implicit. ER
Facula, faculae /ˈfækjʊlə/, /ˈfækjʊli/ Bright spot FA
Farrum, farra /ˈfærəm/, /ˈfærə/ Pancake-like structure, or a row of such structures. Used only on Venus. FR
Flexus, flexūs /ˈflɛksəs/ Very low curvilinear ridge with a scalloped pattern FE
Fluctus, fluctūs /ˈflʌktəs/ Terrain covered by outflow of liquid. Used on Venus, Io and Titan. FL
Flumen, flumina /ˈfluːmɪn/, /ˈfluːmɪnə/ Channel on Titan that might carry liquid FM
Fossa, fossae /ˈfɒsə/, /ˈfɒsi/ Long, narrow, shallow depression FO
Fretum, freta /ˈfriːtəm/, /ˈfriːtə/ Strait of liquid connecting two larger areas of liquid. Used only on Titan. FT
Insula, insulae /ˈɪnsjuːlə/, /ˈɪnsjuːli/ Island (islands), an isolated land area (or group of such areas) surrounded by, or nearly surrounded by, a liquid area (sea or lake). Used only on Titan. IN
Labes, labes /ˈleɪbiːz/ Landslide debris. Used only on Mars. LA
Labyrinthus, labyrinthi /læbɪˈrɪnθəs/, /læbɪˈrɪnθaɪ/ Complex of intersecting valleys or ridges. LB
Lacuna, lacunae /ləˈkjuːnə/, /ləˈkjuːni/ Irregularly shaped depression having the appearance of a dry lake bed. Used only on Titan. LU
Lacus, lacūs /ˈleɪkəs/ A "lake" or small plain on Moon and Mars; on Titan, a "lake" or small, dark plain with discrete, sharp boundaries. LC
Landing site name Lunar features at or near Apollo landing sites LF
Large ringed feature Cryptic ringed features LG
Lenticula, lenticulae /lɛnˈtɪkjʊlə/, /lɛnˈtɪkjʊli/ Small dark spots on Europa LE
Linea, lineae /ˈlɪniə/, /ˈlɪnii/ Dark or bright elongate marking, may be curved or straight LI
Macula, maculae /ˈmækjʊlə/, /ˈmækjʊli/ Dark spot, may be irregular MA
Mare, maria /ˈmɑːri, -reɪ/, /ˈmɑːriə/ A "sea" or large circular plain on Moon and Mars, e.g. Mare Erythraeum; on Titan, large expanses of dark materials thought to be liquid hydrocarbons, e.g. Ligeia Mare. ME
Mensa, mensae /ˈmɛnsə/, /ˈmɛnsi/ A flat-topped prominence with cliff-like edges, i.e. a mesa. MN
Mons, montes /ˈmɒnz/, /ˈmɒntiːz/ Mons refers to a mountain. Montes refers to a mountain range. MO
Oceanus /oʊʃiːˈeɪnəs/ Very large dark area. The only feature with this designation is Oceanus Procellarum. OC
Palus, paludes /ˈpeɪləs/, /pəˈljuːdiːz/ "Swamp"; small plain. Used on the Moon and Mars. PA
Patera, paterae /ˈpætərə/, /ˈpætəri/ Irregular crater, or a complex one with scalloped edges e.g. Ah Peku Patera. Usually refers to the dish-shaped depression atop a volcano. PE
Planitia, planitiae /pləˈnɪʃə/, /pləˈnɪʃi/ Low plain e.g. Amazonis Planitia. PL
Planum, plana /ˈpleɪnəm/, /ˈpleɪnə/ A plateau or high plain e.g. Planum Boreum. PM
Plume A cryovolcanic feature on Triton. This term is currently unused. PU
Promontorium, promontoria /prɒmənˈtɔːriəm/, /prɒmənˈtɔːriə/ "Cape"; headland. Used only on the Moon. PR
Regio, regiones /ˈriːdʒioʊ/ ~ /ˈrɛdʒioʊ/, /rɛdʒiˈoʊniːz/ Large area marked by reflectivity or color distinctions from adjacent areas, or a broad geographic region RE
Reticulum, reticula /rɪˈtɪkjʊləm/, /rɪˈtɪkjʊlə/ Reticular (netlike) pattern on Venus RT
Rima, rimae /ˈraɪmə/, /ˈraɪmi/ Fissure. Used only on the Moon. RI
Rupes, rupes /ˈruːpiːz/ Scarp RU
Satellite feature A feature that shares the name of an associated feature, for example Hertzsprung D. SF
Scopulus, scopuli /ˈskɒpjʊlə/, /ˈskɒpjʊlaɪ/ Lobate or irregular scarp SC
Serpens, serpentes /ˈsɜːrpɛnz/, /sərˈpɛntiːz/ Sinuous feature with segments of positive and negative relief along its length SE
Sinus /ˈsaɪnəs/ "Bay"; small plain on Moon or Mars, e.g. Sinus Meridiani; on Titan, bay within bodies of liquid. SI
Sulcus, sulci /ˈsʌlkəs/, /ˈsʌlsaɪ/ Subparallel furrows and ridges SU
Terra, terrae /ˈtɛrə/, /ˈtɛri/ Extensive land mass e.g. Arabia Terra, Aphrodite Terra. TA
Tessera, tesserae /ˈtɛsərə/, /ˈtɛsəri/ An area of tile-like, polygonal terrain. This term is used only on Venus. TE
Tholus, tholi /ˈθoʊləs/, /ˈθoʊlaɪ/ Small domical mountain or hill e.g. Hecates Tholus. TH
Undae /ˈʌndi/ A field of dunes. Used on Venus, Mars and Titan. UN
Vallis, valles /ˈvælɪs/, /ˈvæliːz/ A valley e.g. Valles Marineris. VA
Vastitas, vastitates /ˈvæstɪtəs/, /væstɪˈteɪtiːz/ An extensive plain. The only feature with this designation is Vastitas Borealis. VS
Virga, virgae /ˈvɜːrɡə/, /ˈvɜːrdʒi/ A streak or stripe of color. This term is currently used only on Titan. VI

By planet

See also

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