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. 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 was assigned in 1919 the task of selecting official names for features on Solar System bodies.
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. 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. 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:- Nomenclature is a tool and the first consideration should be to make it simple, clear, and unambiguous.
- In general, official names will not be given to features whose longest dimensions are less than 100 meters, although exceptions may be made for smaller features having exceptional scientific interest.
- The number of names chosen for each body should be kept to a minimum. Features should be named only when they have special scientific interest, and when the naming of such features is useful to the scientific and cartographic communities at large.
- Duplication of the same surface feature name on two or more bodies, and of the same name for satellites and minor planets, is discouraged. Duplications may be allowed when names are especially appropriate and the chances for confusion are very small.
- 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.
- Where possible, the themes established in early solar system nomenclature should be used and expanded on.
- 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. Where appropriate, the WGPSN strongly supports an equitable selection of names from ethnic groups, countries, and gender on each map; however, a higher percentage of names from the country planning a landing is allowed on landing site maps.
- No names having political, military or religious significance may be used, except for names of political figures prior to the 19th century.
- Commemoration of persons on planetary bodies should not normally be a goal in itself, but may be employed in special circumstances and is reserved for persons of high and enduring international standing. Persons being so honored must have been deceased for at least three years.
- 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.
- 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.
- Accessible and authoritative sources, including Internet sources, are required for adopted names. Wikipedia is not sufficient as a source, but may be useful for identifying appropriate sources.
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 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 are not topographically or geomorphically distinct; the coordinates of these features are identified from an arbitrarily chosen center point. Boundaries may be determined more accurately from geochemical and geophysical data obtained by future missions.
During active missions, small surface features are often given informal names. These may include landing sites, spacecraft impact sites, and small topographic features, such as craters, hills, and rocks. Such names will not be given official status by the IAU, except as provided for by Rule 2 above. As for the larger objects, official names for any such small features would have to conform to established IAU rules and categories.
Descriptor terms (feature types)
Categories for naming features on planets and satellites
Mercury">Mercury (planet)">Mercury
| Feature type | Current list | Naming convention |
| Catenae | list | Radio telescope facilities |
| Craters | list | Famous deceased artists, musicians, painters, authors |
| Dorsa | list | Astronomers who made detailed studies of the planet |
| Facula | list | The word 'snake' in various languages |
| Fossae | list | Significant works of architecture |
| Montes | list | Words for "hot" in various languages. Only one mountain range is currently named: Caloris Montes, from Latin word for "heat" |
| Planitiae | list | Names for Mercury in various languages. Two exceptions exist. |
| Rupēs | list | Ships of discovery or scientific expeditions |
| Valles | list | Abandoned cities, towns or settlements of antiquity |
[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 |
| Paterae | list | Famous women |
| Planitiae | list | Mythological heroines |
| Plana | list | Goddesses of prosperity |
| Regiones | list | Giantesses and Titanesses |
| 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 ; river goddesses |
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. 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. |
| 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 ; cartoon characters ; and '70s music acts.
Deimos">Deimos (moon)">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">Phobos (moon)">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">Amalthea (moon)">Amalthea
People and places associated with the Amalthea mythThebe">Thebe (moon)">Thebe
Features on Thebe are named after people and places associated with the Thebe myth. There is only one named feature on Thebe - Zethus Crater.Io">Io (moon)">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">Europa (moon)">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">Ganymede (moon)">Ganymede
| Feature type | Naming convention |
| Catenae, craters | Gods and heroes of ancient Fertile Crescent people |
| Faculae | Places associated with Egyptian myths |
| Fossae | Gods 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">Callisto (moon)">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">Janus (moon)">Janus
People from myth of Castor and PolluxEpimetheus">Epimetheus (moon)">Epimetheus
People from myth of Castor and PolluxMimas">Mimas (moon)">Mimas
People and places from Malory's Le Morte d'Arthur legends[Enceladus]
People and places from Burton's Arabian NightsTethys">Tethys (moon)">Tethys
People and places from Homer's OdysseyDione">Dione (moon)">Dione
People and places from Virgil's AeneidRhea">Rhea (moon)">Rhea
People and places from creation mythsTitan">Titan (moon)">Titan
| 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 |
| 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 |
| 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 |
| Planitiae and labyrinthi | Names of planets from the Dune series of science fiction novels by American author Frank Herbert |
| Sinūs | Names of terrestrial bays, coves, fjords or other inlets |
| Undae | Gods and goddesses of wind |
| Virgae | Gods and goddesses of rain |
Hyperion">Hyperion (moon)">Hyperion
Sun and Moon deitiesIapetus">Iapetus (moon)">Iapetus
People and places from Sayers' translation of Chanson de Roland, the only exception is Cassini Regio, which is named after its discoverer, Giovanni Cassini.Phoebe">Phoebe (moon)">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]
Satellites of Uranus are named for characters from the works of William Shakespeare.Puck">Puck (moon)">Puck
Mischievous spiritsMiranda">Miranda (moon)">Miranda
Characters, places from Shakespeare's playsAriel">Ariel (moon)">Ariel
Light spiritsUmbriel">Umbriel (moon)">Umbriel
Dark spiritsTitania">Titania (moon)">Titania
Female Shakespearean characters, placesOberon">Oberon (moon)">Oberon
Shakespearean tragic heroes and placesSmall 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">Proteus (moon)">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 crater Pharos.Triton">Triton (moon)">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">Nereid (moon)">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 and plutonian satellites
In February 2017, the IAU approved the following themes for surface features on Pluto and its satellites:[Pluto]
- Gods, goddesses, and other beings associated with the Underworld from mythology, folklore and literature.
- Names for the Underworld and for Underworld locales from mythology, folklore and literature.
- Heroes and other explorers of the Underworld.
- Scientists and engineers associated with Pluto and the Kuiper Belt.
- Pioneering space missions and spacecraft.
- Historic pioneers who crossed new horizons in the exploration of the Earth, sea and sky.
Charon">Charon (moon)">Charon
- Destinations and milestones of fictional space and other exploration.
- Fictional and mythological vessels of space and other exploration.
- Fictional and mythological voyagers, travellers and explorers.
- Authors and artists associated with space exploration, especially Pluto and the Kuiper Belt.
Nix">Nix (moon)">Nix
- Deities of the night.
Hydra">Hydra (moon)">Hydra
- Legendary serpents and dragons.
Kerberos">Kerberos (moon)">Kerberos
- Dogs from literature, mythology, and history.
Styx">Styx (moon)">Styx
- River gods.
[Asteroid]s
[1 Ceres]
| Feature type | Naming convention |
| Craters | Agricultural deities |
| other | Agricultural festivals |
[4 Vesta]
| Feature type | Naming convention |
| Craters | Historical and mythological women of Ancient Rome |
| other | Festivals of Ancient Rome |
[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">Dactyl (asteroid)">(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 |