Planetary nomenclature

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. The task of assigning official names to features is taken up by the International Astronomical Union since its founding in 1919.^[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 religious significance may be used, except for names of political figures prior to the 19th century. (Note: Apparently this only goes for religions that are widely practiced today, since gods and goddesses of ancient religions are obviously acceptable to the IAU.)
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	Description	Designation
Albedo feature	An area which shows a contrast in brightness or darkness (albedo) with adjacent areas. This term is implicit.	AL
Arcus, arcūs	Arc: curved feature	AR
Astrum, astra	Radial-patterned features on Venus	AS
Catena, catenae	A chain of craters e.g. Enki Catena.	CA
Cavus, cavi	Hollows, irregular steep-sided depressions usually in arrays or clusters	CB
Chaos	A distinctive area of broken or jumbled terrain e.g. Iani Chaos.	CH
Chasma, chasmata	Deep, elongated, steep-sided depression e.g. Eos Chasma.	CM
Colles	A collection of small hills or knobs.	CO
Corona, coronae	An oval feature. Used only on Venus and Miranda.	CR
Crater, craters	A circular depression likely created by impact event. This term is implicit.	AA
Dorsum, dorsa	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	Bright spot	FA
Farrum, farra	Pancake-like structure, or a row of such structures	FR
Flexus, flexūs	Very low curvilinear ridge with a scalloped pattern	FE
Fluctus, fluctūs	Terrain covered by outflow from a volcano.	FL
Flumen, flumina	Channel on Titan that might carry liquid	FM
Fossa, fossae	Long, narrow, shallow depression	FO
Insula, insulae	Island (islands), an isolated land area (or group of such areas) surrounded by, or nearly surrounded by, a liquid area (sea or lake). The only feature with this designation is Mayda Insula.	IN
Labes, labēs	Landslide debris. Used only on Mars.	LA
Labyrinthus, labyrinthi	Complex of intersecting valleys or ridges.	LB
Lacus	A "lake" or small plain. Used on the Moon, Mars and Titan.	LC
Landing site name	Lunar features at or near Apollo landing sites	LF
Large ringed feature	Cryptic ringed features	LG
Lenticula, lenticulae	Small dark spots on Europa	LE
Linea, lineae	Dark or bright elongate marking, may be curved or straight	LI
Macula, maculae	Dark spot, may be irregular	MA
Mare, maria	A "sea" or large circular plain e.g. Mare Erythraeum. Used on the Moon, Mars and Titan.	ME
Mensa, mensae	A flat-topped prominence with cliff-like edges, i.e. a mesa.	MN
Mons, montes	Mons refers to a mountain. Montes refers to a mountain range.	MO
Oceanus	Very large dark area. Used only on the Moon.	OC
Palus, paludes	"Swamp"; small plain. Used on the Moon and Mars.	PA
Patera, paterae	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	Low plain e.g. Amazonis Planitia.	PL
Planum, plana	A plateau or high plain e.g. Planum Boreum.	PM
Plume	A cryovolcanic feature on Triton. This term is currently unused.	PU
Promontorium, promontoria	"Cape"; headland. Used only on the Moon.	PR
Regio, regiones	Large area marked by reflectivity or color distinctions from adjacent areas, or a broad geographic region	RE
Reticulum, reticula	reticular (netlike) pattern on Venus	RT
Rima, rimae	Fissure. Used only on the Moon.	RI
Rupes, rupēes	Scarp	RU
Satellite feature	A feature that shares the name of an associated feature, for example Hertzsprung D.	SF
Scopulus, scopuli	Lobate or irregular scarp	SC
Serpens, serpentes	Sinuous feature with segments of positive and negative relief along its length	SE
Sinus	"Bay"; small plain e.g. Sinus Meridiani.	SI
Sulcus, sulci	Subparallel furrows and ridges	SU
Terra, terrae	Extensive land mass e.g. Arabia Terra.	TA
Tessera, tesserae	An area of tile-like, polygonal terrain. This term is used only on Venus.	TE
Tholus, tholi	Small domical mountain or hill e.g. Hecates Tholus.	TH
Undae	A field of dunes.	UN
Vallis, valles	A valley e.g. Valles Marineris.	VA
Vastitas, vastitates	An extensive plain. The only feature with this designation is Vastitas Borealis.	VS
Virga, virgae	A streak or stripe of color	VI

Categories for naming features on planets and satellites

Mercury

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

Venus

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	Goddesses, miscellaneous
Chasmata	list	Goddesses of hunt; moon goddesses
Colles	list	Sea goddesses
Coronae	list	Fertility and earth goddesses
Craters	list	Over 20 km; famous women; under 20 km, common female first names
Dorsa	list	Sky goddesses
Farra	list	Water goddesses
Fluctūs	list	Goddesses, miscellaneous
Fossae	list	Goddesses of war
Labyrinthi	list	Goddesses, miscellaneous
Lineae	list	Goddesses of war
Montes	list	Goddesses, miscellaneous (also one radar scientist)
Paterae	list	Famous women
Planitiae	list	Mythological heroines
Plana	list	Goddesses of prosperity
Regiones	list	Giantesses and Titanesses (also two Greek alphanumeric)
Rupēs	list	Goddesses of hearth and home
Terrae	list	Goddesses of love
Tesserae	list	Goddesses of fate and fortune
Tholi	list	Goddesses, miscellaneous
Undae	list	Desert goddesses
Valles	list	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

Mars

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).^[3]

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.

Phobos

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

Amalthea

People and places associated with the Amalthea myth

Thebe

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

Io

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.

Europa

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

Ganymede

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

Callisto

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

Janus

People from myth of Castor and Pollux (twins)

Epimetheus

People from myth of Castor and Pollux (twins)

Mimas

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

Enceladus

People and places from Burton's Arabian Nights

Tethys

People and places from Homer's Odyssey

Dione

People and places from Virgil's Aeneid

Rhea

People and places from creation myths

Titan

Feature type	Naming convention
Major bright albedo features	Sacred or enchanted places from legends, myths, stories, and poems of cultures from around the world
Major dark albedo features	Legendary/mythical primordial seas or enchanted waters from world cultures
Craters (and lakes if present)	Lakes from all continents on Earth
Fluvial channels	Rivers from all continents on Earth
Other features	Deities of happiness, peace, and harmony from world cultures

Hyperion

Sun and Moon deities

Iapetus

People and places from Sayers' translation of Chanson de Roland

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

Puck

Mischievous (Pucklike) spirits (class)

Miranda

Characters, places from Shakespeare's plays

Ariel

Light spirits (individual and class)

Umbriel

Dark spirits (individual)

Titania

Female Shakespearean characters, places

Oberon

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

Proteus

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.

Triton

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.

Nereid

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.

Pluto

There are currently no named features on Pluto because it is extremely difficult to resolve surface features with current telescopes.^[4][5] When discovered, either by telescopic observation or the New Horizons flyby in 2015, Plutonian surface features are to be named after underworld deities.

Asteroids

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

Notes

See also

• Astronomical naming conventions
• Geological features of the solar system
• List of adjectivals and demonyms of astronomical bodies
• Naming of moons
• Selenography
• Toponymy, the scientific study of place-names (toponyms), their origins, meanings, use and typology.

References

• The above article incorporates text from the United States Geological Survey Gazetteer of Planetary Nomenclature, which is in the public domain.
• Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature, E. A. Whitaker, 1999, ISBN 0-521-62248-4.

Further reading

• Ronald Greeley and Raymond M. Batson (1990). Planetary Mapping. Cambridge University Press. ISBN 0-521-03373-X. 

External links

• Gazetteer of Planetary Nomenclature IAU Working Group for Planetary System Nomenclature (WGPSN)
• 'Planetary Names: How do we come up with them?', Planetary Society weblog article by Rosaly Lopes, IAU WGPSN member
• Members of the WGPSN
• Planetary Maps: Visualization and Nomenclature Cartographica 41/2 2006
• Development of a Local Toponym System at the Mars Desert Research Station Cartographica 42/2 2007
• APTN National News interviews Planetary Cartographer John Koulouris,(Esq.) on I.A.U. officially adopted Planetary Surface Feature Nomenclature attributed to Aboriginal Peoples' Cultures, People and Places
• Planetary Atlas of Venus in the Hellenic (Greek) and English Languages with I.A.U. adopted surface feature nomenclature as of 1984 created by: John A. Koulouris,(Esq.)