Planetary nomenclature

Planetary nomenclature, like terrestrial nomenclature, is used to uniquely identify a feature on the surface of a planet or natural satellite so that the feature can be easily located, described, and discussed.

Table of contents 1 How names are approved 2 IAU Rules and Conventions 3 Naming Conventions 4 Descriptor Terms (Feature Types) 5 Categories for naming features on planets and satellites 5.1 Mercury 5.2 Venus 5.3 The Moon 5.4 Mars and martian satellites 5.4.1 Mars 5.4.2 Deimos 5.4.3 Phobos 5.5 Satellites of Jupiter 5.5.1 Amalthea 5.5.2 Thebe 5.5.3 Io 5.5.4 Europa 5.5.5 Ganymede 5.5.6 Callisto 5.6 Satellites of Saturn 5.6.1 Janus 5.6.2 Epimetheus 5.6.3 Mimas 5.6.4 Enceladus 5.6.5 Tethys 5.6.6 Dione 5.6.7 Rhea 5.6.8 Titan 5.6.9 Hyperion 5.6.10 Iapetus 5.6.11 Phoebe 5.7 Satellites of Uranus 5.7.1 Puck 5.7.2 Miranda 5.7.3 Ariel 5.7.4 Umbriel 5.7.5 Titania 5.7.6 Oberon 5.7.7 Small satellites 5.8 Satellites of Neptune 5.8.1 Proteus 5.8.2 Triton 5.8.3 Nereid 5.8.4 Small satellites 5.9 Pluto 5.10 Asteroids 5.10.1 243 Ida 5.10.2 Dactyl 5.10.3 951 Gaspra 5.10.4 253 Mathilde 5.10.5 433 Eros

How names are approved

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. 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 meets triennially. 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:

1. Nomenclature is a tool and the first consideration should be to make it simple, clear, and unambiguous.
2. 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.
3. Duplication of the same name on two or more bodies is to be avoided.
4. 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.
5. Where possible, the themes established in early solar system nomenclature should be used and expanded on.
6. 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.
7. No names having political, military or religious significance may be used, except for names of political figures prior to the 19th century.
8. 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.
9. 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.
10. 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 channels (valles) on Mars and craters on the Moon, Mars, and Venus; naming conventions for these features differ according to size. The categories for naming features on each planet or satellite (and the exceptions) are listed in Appendix 6. 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		AL
Astrum, astra	Radial-patterned features on Venus	AS
Catena, catenae	Chain of craters	CA
Cavus, cavi	Hollows, irregular steep-sided depressions usually in arrays or clusters	CB
Chaos	Distinctive area of broken terrain	CH
Chasma, chasmata	A deep, elongated, steep-sided depression	CM
Colles	Small hills or knobs	CO
Corona, coronae	Ovoid-shaped feature	CR
Crater, craters	A circular depression	AA
Dorsum, dorsa	Ridge	DO
Eruptive center	Active volcanic centers on Io	ER
Facula, faculae	Bright spot	FA
Farrum, farra	Pancake-like structure, or a row of such structures	FR
Flexus, flex-us	A very low curvilinear ridge with a scalloped pattern	FE
Fluctus, fluct-us	Flow terrain	FL
Fossa, fossae	Long, narrow, shallow depression	FO
Labes, lab-es	Landslide	LA
Labyrinthus, labyrinthi	Complex of intersecting valleys	LB
Lacus(1)	"Lake"; small plain	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	A dark or bright elongate marking, may be curved or straight	LI
Macula, maculae	Dark spot, may be irregular	MA
Mare(1), maria	"Sea"; large circular plain	ME
Mensa, mensae	A flat-topped prominence with cliff-like edges	MN
Mons, montes	Mountain	MO
Oceanus(1)	A very large dark area on the moon	OC
Palus(1), paludes	"Swamp"; small plain	PA
Patera, paterae	An irregular crater, or a complex one with scalloped edges	PE
Planitia, planitiae	Low plain	PL
Planum, plana	Plateau or high plain	PM
Plume		PU
Promontorium(1), promontoria	"Cape"; headland	PR
Regio, regiones	A 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(1)	Fissure	RI
Rupes, rup-es	Scarp	RU
Scopulus, scopuli	Lobate or irregular scarp	SC
Sinus	"Bay"; small plain	SI
Sulcus, sulci	Subparallel furrows and ridges	SU
Terra, terrae	Extensive land mass	TA
Tessera, tesserae	Tile-like, polygonal terrain	TE
Tholus, tholi	Small domical mountain or hill	TH
Undae	Dunes	UN
Vallis, valles	Valley	VA
Vastitas, vastitates	Extensive plain	VS

(1) Used only on the Moon

Categories for naming features on planets and satellites

Mercury

Craters	Famous deceased artists, musicians, painters, authors
Montes	Caloris, from Latin word for "hot"
Planitiae	Names for Mercury (either planet or god) in various languages
Rup-es	Ships of discovery or scientific expeditions
Valles	Radio telescope facilities

Venus

Astra	Goddesses, miscellaneous
Chasmata	Goddesses of hunt; moon goddesses
Colles	Sea goddesses
Coronae	Fertility and earth goddesses
Craters	Over 20 km; famous women; under 20 km, common female first names
Dorsa	Sky goddesses
Farrum	Water goddesses
Fluct-us	Goddesses, miscellaneous
Fossae	Goddesses of war
Labyrinthus	Goddesses, miscellaneous
Lineae	Goddesses of war
Montes	Goddesses, miscellaneous (also one radar scientist)
Paterae	Famous women
Planitiae	Mythological heroines
Planum	Goddesses of prosperity
Regiones	Giantesses and Titanesses (also two Greek alphanumeric)
Rup-es	Goddesses of hearth and home
Tesserae	Goddesses of fate and fortune
Terrae	Goddesses of love
Tholi	Goddesses, miscellaneous
Undae	Desert goddesses
Valles	Word for planet Venus in various world languages (400 km and longer); river goddesses (less than 400 km in length)

The Moon

Craters, Catenae, Dorsa, Rimae	Large craters: famous deceased scientists, scholars, artists; small craters: common first names. Other features named from nearby craters
Lac-us, Maria, Paludes, Sin-us	Latin terms describing weather and other abstract concepts
Montes	Terrestrial mountain ranges or nearby craters
Rup-es	Names of nearby mountain ranges (terrestrial names)
Valles	Name of nearby features

Mars and martian satellites

Mars

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

Deimos

Authors who wrote about Martian satellites

Phobos

Scientists involved with the discovery, dynamics, or properties of the Martian satellites

Satellites of Jupiter

Amalthea

People and places associated with the Amalthea myth

Thebe

People and places associated with the Thebe myth

Io

Active eruptive centers	Fire, sun, thunder gods and heroes
Catenae	Sun gods
Fluct-us	Name derived from nearby named feature, or fire, sun, thunder, volcano gods, goddesses and heroes, mythical blacksmiths
Mensae	People associated with Io myth, derived from nearby feature, or from Dante's Inferno
Montes	Places associated with Io myth, derived from nearby feature, or from Dante's Inferno
Paterae	Fire, sun, thunder, volcano gods, heroes, goddesses, mythical blacksmiths
Plana	Places associated with Io myth, derived from nearby feature, or from Dante's Inferno
Regiones	Places associated with Io myth, derived from nearby feature, or from Dante's Inferno
Tholi	Places associated with Io myth, derived from nearby feature, or from Dante's Inferno

Europa

Chaos	Places associated with Celtic myths
Craters	Celtic gods and heroes
Flex-us	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

Catenae	Gods and heroes of ancient Fertile Crescent people
Craters	Gods and heroes of ancient Fertile Crescent people
Faculae	Places associated with Egyptian myths
Fossae	Gods (or principals) of ancient Fertile Crescent people
Regiones	Astronomers who discovered Jovian satellites
Sulci	Places associated with myths of ancient people

Callisto

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

Ancient displaced cultures

Hyperion

Sun and Moon deities

Iapetus

People and places from Sayers' translation of Chanson de Roland

Phoebe

People associated with Phoebe, islands of the Greek archipelagos

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

Heroines from Shakespeare and Pope

Satellites of Neptune

Proteus

Water-related spirits, gods, goddesses (excluding Greek and Roman names)

Triton

Aquatic names, excluding Roman and Greek. Possible categories include worldwide aquatic spirits, famous terrestrial fountains or fountain locations, terrestrial aquatic features, famous terrestrial geysers or geyser locations, terrestrial islands.

Nereid

Individual nereids

Small satellites

Gods and goddesses associated with Neptune/Poseidon mythology or generic mythological aquatic beings

Pluto

Underworld deities

Asteroids

243 Ida

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

Dactyl

Craters

Idaean dactyls

951 Gaspra

Craters	Spas of the world
Regiones	Discoverer of Gaspra, and Galileo project participants

253 Mathilde

Craters

Coal fields and basins of the world

433 Eros

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

Contents adapted from the public domain work United States Geological Survey Gazetteer of Planetary Nomenclature (http://planetarynames.wr.usgs.gov/)