Planetary nomenclature

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A map of the Moon from Andrees Allgemeiner Handatlas, 1st edition (1881), predating IAU conventions

Planetary nomenclature, like terrestrial nomenclature, is a system of uniquely identifying features on the surface of a planet or natural satellite so that the features can be easily located, described, and discussed. Since the invention of the telescope, astronomers have given names to the surface features they have discerned, especially on the Moon and Mars. To standardize planetary nomenclature, the International Astronomical Union (IAU) was assigned in 1919 the task of selecting official names for features on solar system bodies.[1]

How names are approved by the IAU

When images are first obtained of the surface of a planet or satellite, a theme for naming features is chosen and a few important features are named, usually by members of the appropriate IAU task group (a commonly accepted planet-naming group). Later, as higher resolution images and maps become available, additional features are named at the request of investigators mapping or describing specific surfaces, features, or geologic formations. Anyone may suggest that a specific name be considered by a task group. If the members of the task group agree that the name is appropriate, it can be retained for use when there is a request from a member of the scientific community that a specific feature be named. Names successfully reviewed by a task group are submitted to the IAU Working Group for Planetary System Nomenclature (WGPSN). Upon successful review by the members of the WGPSN, names are considered provisionally approved and can be used on maps and in publications as long as the provisional status is clearly stated. Provisional names are then presented for adoption to the IAU's General Assembly, which met triennially in the past, and which now adopts nomenclature for planetary surface features as required. A name is not considered to be official — that is, "adopted" — until the General Assembly has given its approval.

IAU rules and conventions

Names adopted by the IAU must follow various rules and conventions established and amended through the years by the Union. These include:[2]

  1. Nomenclature is a tool and the first consideration should be to make it simple, clear, and unambiguous.
  2. Features whose longest dimension is less than 100 meters are not assigned official names unless they have exceptional scientific interest.
  3. The number of names chosen for each body should be kept to a minimum, and their placement governed by the requirements of the scientific community.
  4. Duplication of the same name on two or more bodies is to be avoided.
  5. Individual names chosen for each body should be expressed in the language of origin. Transliteration for various alphabets should be given, but there will be no translation from one language to another.
  6. Where possible, the themes established in early solar system nomenclature should be used and expanded on.
  7. Solar system nomenclature should be international in its choice of names. Recommendations submitted to the IAU national committees will be considered, but final selection of the names is the responsibility of the International Astronomical Union. The WGPSN strongly supports equitable selection of names from ethnic groups/countries on each map; however, a higher percentage of names from the country planning a landing is allowed on landing site maps.
  8. No names having political, military or (modern) religious significance may be used, except for names of political figures prior to the 19th century.
  9. Commemoration of persons on planetary bodies should not be a goal in itself but should be reserved for persons of high and enduring international standing. Persons being so honored must have been deceased for at least three years.
  10. When more than one spelling of a name is extant, the spelling preferred by the person, or used in an authoritative reference, should be used. Diacritical marks are a necessary part of a name and will be used.
  11. Ring and ring-gap nomenclature and names for newly discovered satellites are developed in joint deliberation between WGPSN and IAU Commission 20. Names will not be assigned to satellites until their orbital elements are reasonably well known or definite features have been identified on them.

In addition to these general rules, each task group develops additional conventions as it formulates an interesting and meaningful nomenclature for individual planetary bodies.

Naming conventions

Names for all planetary features include a descriptor term, with the exception of two feature types. For craters, the descriptor term is implicit. Some features named on Io and Triton do not carry a descriptor term because they are ephemeral.

In general, the naming convention for a feature type remains the same regardless of its size. Exceptions to this rule are valleys and craters on Mars and Venus; naming conventions for these features differ according to size.

One feature classification, regio, was originally used on early maps of the Moon and Mercury (drawn from telescopic observations) to describe vague albedo features. It is now used to delineate a broad geographic region.

Named features on bodies so small that coordinates have not yet been determined are identified on drawings of the body that are included in the IAU Transactions volume of the year when the names were adopted. Satellite rings and gaps in the rings are named for scientists who have studied these features; drawings that show these names are also included in the pertinent Transactions volume. Names for atmospheric features are informal at present; a formal system will be chosen in the future.

The boundaries of many large features (such as terrae, regiones, planitiae and plana) are not topographically or geomorphically distinct; the coordinates of these features are identified from an arbitrarily chosen center point. Boundaries (and thus coordinates) may be determined more accurately from geochemical and geophysical data obtained by future missions.

Descriptor terms (feature types)

Feature Pronunciation[3] Description Designation
Albedo feature /ælˈbd/ 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 /kəˈtnə/, /kəˈtn/ A chain of craters e.g. Enki Catena. CA
Cavus, cavi /ˈkvəs/, /ˈkv/ Hollows, irregular steep-sided depressions usually in arrays or clusters CB
Chaos /ˈk.ɒs/ 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 /ˈkɒlz/ A collection of small hills or knobs. CO
Corona, coronae /kɒˈrnə/, /kɒˈrn/ An oval feature. Used only on Venus and Miranda. CR
Crater, craters /ˈkrtər/ 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/, /ˈfækjʊl/ 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 /ˈflmn/, /ˈflmnə/ Channel on Titan that might carry liquid FM
Fossa, fossae /ˈfɒsə/, /ˈfɒs/ Long, narrow, shallow depression FO
Fretum, freta /ˈfrtəm/, /ˈfrtə/ Strait of liquid connecting two larger areas of liquid. Used only on Titan. FT
Insula, insulae /ˈɪnsjlə/, /ˈɪnsjl/ 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 /ˈlbz/ Landslide debris. Used only on Mars. LA
Labyrinthus, labyrinthi /læbˈrɪnθəs/, /læbˈrɪnθ/ Complex of intersecting valleys or ridges. LB
Lacuna, lacunae /ləˈkjuːnə/, /ləˈkjuːn/ Irregularly shaped depression having the appearance of a dry lake bed. Used only on Titan. LU
Lacus, lacūs /ˈlkəs/ 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/, /lɛnˈtɪkjʊl/ Small dark spots on Europa LE
Linea, lineae /ˈlɪnə/, /ˈlɪn./ Dark or bright elongate marking, may be curved or straight LI
Macula, maculae /ˈmækjʊlə/, /ˈmækjʊl/ Dark spot, may be irregular MA
Mare, maria /ˈmɑːr/ ~ /ˈmɑːr/, /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/, /ˈmɛns/ A flat-topped prominence with cliff-like edges, i.e. a mesa. MN
Mons, montes /ˈmɒnz/, /ˈmɒntz/ Mons refers to a mountain. Montes refers to a mountain range. MO
Oceanus /ʃˈnəs/ Very large dark area. The only feature with this designation is Oceanus Procellarum. OC
Palus, paludes /ˈpləs/, /pəˈlʲdz/ "Swamp"; small plain. Used on the Moon and Mars. PA
Patera, paterae /ˈpætərə/, /ˈpætər/ 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/, /pləˈnɪʃ/ Low plain e.g. Amazonis Planitia. PL
Planum, plana /ˈplnəm/, /ˈplnə/ A plateau or high plain e.g. Planum Boreum. PM
Plume A cryovolcanic feature on Triton. This term is currently unused. PU
Promontorium, promontoria /prɒmənˈtɔəriəm/, /prɒmənˈtɔəriə/ "Cape"; headland. Used only on the Moon. PR
Regio, regiones /ˈr/ ~ /ˈrɛ/, /rɛiˈnz/ Large area marked by reflectivity or color distinctions from adjacent areas, or a broad geographic region RE
Reticulum, reticula /rˈtɪkjʊləm/, /rˈtɪkjʊlə/ reticular (netlike) pattern on Venus RT
Rima, rimae /ˈrmə/, /ˈrm/ Fissure. Used only on the Moon. RI
Rupes, rupes /ˈrpz/ Scarp RU
Satellite feature A feature that shares the name of an associated feature, for example Hertzsprung D. SF
Scopulus, scopuli /ˈskɒpjʊlə/, /ˈskɒpjʊl/ Lobate or irregular scarp SC
Serpens, serpentes /ˈsɜːrpɛnz/, /sərˈpɛntz/ Sinuous feature with segments of positive and negative relief along its length SE
Sinus /ˈsnəs/ "Bay"; small plain on Moon or Mars, e.g. Sinus Meridiani; On Titan, bay within bodies of liquid. SI
Sulcus, sulci /ˈsʌlkəs/, /ˈsʌls/ Subparallel furrows and ridges SU
Terra, terrae /ˈtɛrə/, /ˈtɛr/ Extensive land mass e.g. Arabia Terra, Aphrodite Terra. TA
Tessera, tesserae /ˈtɛsərə/, /ˈtɛsər/ An area of tile-like, polygonal terrain. This term is used only on Venus. TE
Tholus, tholi /ˈθləs/, /ˈθl/ Small domical mountain or hill e.g. Hecates Tholus. TH
Undae /ˈʌnd/ A field of dunes. Used on Venus, Mars and Titan. UN
Vallis, valles /ˈvæls/, /ˈvælz/ A valley e.g. Valles Marineris. VA
Vastitas, vastitates /ˈvæsttəs/, /væstˈttz/ An extensive plain. The only feature with this designation is Vastitas Borealis. VS
Virga, virgae /ˈvɜːrɡə/, /ˈvɜːr/ A streak or stripe of color. This term is currently used only on Titan. VI

Categories for naming features on planets and satellites


Examples of Mercurian nomenclature from the Kuiper quadrangle.
Feature type Current list Naming convention
Craters list [1] Famous deceased artists, musicians, painters, authors
Dorsa list [2] Astronomers who made detailed studies of the planet
Fossae list [3] Significant works of architecture
Montes list [4] Words for "hot" in various languages. Only one mountain is currently named: Caloris Montes, from Latin word for "heat"
Planitiae list [5] Names for Mercury (either planet or god) in various languages
Rupēs list [6] Ships of discovery or scientific expeditions
Valles list [7] Radio telescope facilities


All but three features on Venus are named after females. These three exceptions were named before the convention was adopted, being respectively Alpha Regio, Beta Regio, and Maxwell Montes which is named after James Clerk Maxwell.

Feature type Current list Naming convention
Astra none [8] Goddesses, miscellaneous
Chasmata list [9] Goddesses of hunt; moon goddesses
Colles list [10] Sea goddesses
Coronae list [11] Fertility and earth goddesses
Craters list [12] Over 20 km; famous women; under 20 km, common female first names
Dorsa list [13] Sky goddesses
Farra list [14] Water goddesses
Fluctūs list [15] Goddesses, miscellaneous
Fossae list [16] Goddesses of war
Labyrinthi list [17] Goddesses, miscellaneous
Lineae list [18] Goddesses of war
Montes list [19] Goddesses, miscellaneous (also one radar scientist)
Paterae list [20] Famous women
Planitiae list [21] Mythological heroines
Plana list [22] Goddesses of prosperity
Regiones list [23] Giantesses and Titanesses (also two Greek alphanumeric)
Rupēs list [24] Goddesses of hearth and home
Terrae list [25] Goddesses of love
Tesserae list [26] Goddesses of fate and fortune
Tholi list [27] Goddesses, miscellaneous
Undae list [28] Desert goddesses
Valles list [29] Word for planet Venus in various world languages (400 km and longer); river goddesses (less than 400 km in length)

The Moon

Feature type Naming convention
Craters Craters are generally named after deceased scientists, scholars, artists and explorers who have made outstanding or fundamental contributions to their field. Additionally, craters in or around Mare Moscoviense are named after deceased Russian cosmonauts and craters in and around Apollo crater are named after deceased American astronauts (see Space accidents and incidents). This convention may be extended if other space-faring countries suffer fatalities in spaceflight.
Lacūs, Maria, Paludes, Sinūs These features are assigned names which are Latin terms describing weather and other abstract concepts.
Montes Montes are named after terrestrial mountain ranges or nearby craters.
Rupēs Rupēs are named after nearby mountain ranges (see above).
Valles Valles are named after nearby features.
Others Features that don't fall into any of the above categories are named after nearby craters.

Mars and martian satellites


Early map of Mars by Giovanni Schiaparelli, which depicts classical albedo features
Feature type Naming convention
Large craters Deceased scientists who have contributed to the study of Mars; writers and others who have contributed to the lore of Mars
Small craters Villages of the world with a population of less than 100,000.
Large valles Name for Mars/star in various languages
Small valles Classical or modern names of rivers
Other features From nearest named albedo feature on Schiaparelli or Antoniadi maps. See Classical albedo features on Mars for a list.

When space probes have landed on Mars, individual small features such as rocks, dunes, and hollows have often been given informal names. Many of these are frivolous: features have been named after ice cream (such as Cookies N Cream); cartoon characters (such as SpongeBob SquarePants and Patrick); and '70s music acts (such as ABBA and the Bee Gees).[4]


The two named craters on Deimos

Features on Deimos are named after authors who wrote about Martian satellites. There are currently two named features on Deimos - Swift crater and Voltaire crater - after Jonathan Swift and Voltaire who predicted the presence of Martian moons.


All features on Phobos are named after scientists involved with the discovery, dynamics, or properties of the Martian satellites or people and places from Jonathan Swift's Gulliver's Travels.

Satellites of Jupiter


People and places associated with the Amalthea myth


Features on Thebe are named after people and places associated with the Thebe myth. There is only one named feature on Thebe - Zethus Crater.


Feature type Naming convention
Active eruptive centers Active volcanoes on Io are named after fire, sun or thunder gods or heroes.
Catenae Crater chains are named after Sun gods.
Fluctūs Names of fluctūs are derived from a nearby named feature, fire, sun, thunder or volcano gods, goddesses and heroes or mythical blacksmiths.
Mensae, Montes, Plana, Regiones and Tholi These features can be named after places associated with Io mythology, derived from nearby named features, or places from Dante's Inferno
Paterae Paterae on Io are named after fire, sun, thunder or volcano gods, heroes or goddesses or mythical blacksmiths.
Valles Names of valleys are derived from nearby named features.


Feature type Naming convention
Chaos Places associated with Celtic myths
Craters Celtic gods and heroes
Flexūs Places associated with the Europa myth
Large ringed features Celtic stone circles
Lenticulae Celtic gods and heroes
Lineae People associated with the Europa myth
Maculae Places associated with the Europa myth
Regiones Places associated with Celtic myths


Feature type Naming convention
Catenae, craters Gods and heroes of ancient Fertile Crescent people
Faculae Places associated with Egyptian myths
Fossae Gods (or principals) of ancient Fertile Crescent people
Paterae Paterae on Ganymede are named after wadis in the Fertile Crescent.
Regiones Astronomers who discovered Jovian satellites
Sulci Places associated with myths of ancient people


Feature type Naming convention
Large ringed features Homes of the gods and of heroes
Craters Heroes and heroines from northern myths
Catenae Mythological places in high latitudes

Satellites of Saturn


People from myth of Castor and Pollux (twins)


People from myth of Castor and Pollux (twins)


People and places from Malory's Le Morte d'Arthur legends (Baines translation)


People and places from Burton's Arabian Nights


People and places from Homer's Odyssey


People and places from Virgil's Aeneid


People and places from creation myths


Feature type Naming convention
Albedo features, terrae Sacred or enchanted places, paradise, or celestial realms from legends, myths, stories, and poems of cultures from around the world
Colles Names of characters from Middle-earth, the fictional setting in fantasy novels by English author J.R.R. Tolkien (1892-1973)
Craters and ringed features Gods and goddesses of wisdom
Facula and faculae Facula: Names of islands on Earth that are not politically independent, Faculae: Names of archipelagos
Fluctūs Gods and goddesses of beauty
Flumina Names of mythical or imaginary rivers
Freta Names of characters from the Foundation series of science fiction novels by American author Isaac Asimov (1920-1992)
Insulae Names of islands from legends and myths
Lacūs and lacunae Lakes on Earth, preferably with a shape similar to the lacus or lacuna on Titan
Mare and maria Sea creatures from myth and literature
Montes Names of mountains and peaks from Middle-earth, the fictional setting in fantasy novels by English author J.R.R. Tolkien (1892-1973)
Planitiae and labyrinthi Names of planets from the Dune series of science fiction novels by American author Frank Herbert (1920 - 1986)
Sinūs Names of terrestrial bays, coves, fjords or other inlets
Undae Gods and goddesses of wind
Virgae Gods and goddesses of rain


Sun and Moon deities


People and places from Sayers' translation of Chanson de Roland, the only exception is Cassini Regio, which is named after its discoverer, Giovanni Cassini.


Examples of crater nomenclature on Phoebe
Feature type Naming convention
Craters Craters of Phoebe are named after people associated with Phoebe or people from Argonautica by Apollonius Rhodius or Gaius Valerius Flaccus.
Other Non-crater features on Phoebe are named after places from Argonautica.

Satellites of Uranus


Mischievous (Pucklike) spirits (class)


Characters, places from Shakespeare's plays


Light spirits (individual and class)


Dark spirits (individual)


Female Shakespearean characters, places


Shakespearean tragic heroes and places

Small satellites

There are currently no named features on Uranian small satellites, however the naming convention is heroines from plays by Shakespeare and Pope.

Satellites of Neptune


Features on Proteus are to be named after water-related spirits, gods or goddesses who are neither Greek nor Roman. The only named feature on Proteus is Pharos.


Geological features on Triton should be assigned aquatic names, excluding those which are Roman and Greek in origin. Possible themes for individual descriptor terms include worldwide aquatic spirits, famous terrestrial fountains or fountain locations, terrestrial aquatic features, famous terrestrial geysers or geyser locations and terrestrial islands.


There are currently no named features on Nereid. When features are discovered, they are to be named after individual nereids.

Small satellites

Features on other satellites of Neptune, once discovered, should be named after gods and goddesses associated with Neptune/Poseidon mythology or generic mythological aquatic beings.



243 Ida

Feature type Naming convention
Craters Caverns and grottos of the world
Dorsa Galileo project participants
Regiones Discoverer of Ida and places associated with the discoverer

(243) Ida I Dactyl

Feature type Naming convention
Craters Idaean dactyls

951 Gaspra

Feature type Naming convention
Craters Spas of the world
Regiones Discoverer of Gaspra, and Galileo project participants

253 Mathilde

Feature type Naming convention
Craters Coal fields and basins of the world

433 Eros

Feature type Naming convention
Craters Mythological and legendary names of an erotic nature
Regiones Discoverers of Eros
Dorsa Scientists who have contributed to the exploration and study of Eros

25143 Itokawa

See also


  1. "History of Planetary Nomenclature". 2008-05-17.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. Planetary Names: IAU Rules and Conventions, IAU<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. Listed pronunciations are conventional or follow the traditional English pronunciation of Latin words. However, some speakers use different (often variable) pronunciations that are closer to the Latin or Greek.
  4. Chong, Jia-Rui (2005-10-09). "Map of Mars fills up with strange names". Pittsburgh Post-Gazette. Retrieved 2008-04-18.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>


Further reading

  • Ronald Greeley & Raymond M. Batson (1990). Planetary Mapping. Cambridge University Press. ISBN 0-521-03373-X.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links