Planetary nomenclature

Planetary nomenclature is a special way to give names to places on the surface of planets and moons. Just like we have names for cities and mountains here on Earth, scientists need names to talk about features on other worlds. This helps everyone know exactly where something is and what it looks like.

Ever since people started using telescopes, they've been spotting interesting spots on nearby worlds like the Moon and Mars. Each of these spots needed a name so scientists could study them and share their discoveries.

To make sure everyone used the same names and rules, a group called the International Astronomical Union was created in 1919. The IAU decided on naming rules for all the bumps, craters, and valleys on Solar System bodies. Thanks to this system, whether you're looking at pictures of Venus or Jupiter's moon Europa, you can be sure everyone is talking about the same place when they use its name.

IAU approval procedure

When we first see pictures of a planet or moon, scientists pick a theme for naming its features and give names to a few important spots. These names are usually chosen by special groups of experts. As we get better pictures, more features get named based on suggestions from scientists studying those places.

Anyone can suggest a name, and if the experts think it’s a good fit, they pass it along to the International Astronomical Union’s special naming group. Once this group approves, the name becomes official and can be used on maps and in science books. All the approved names are listed in a special book called the Gazetteer of Planetary Nomenclature.

IAU rules and conventions

The International Astronomical Union (IAU) has created rules to help give names to features on planets and moons. These rules make sure names are simple, clear, and not confusing.

Names are only given to features that are bigger than 100 meters or have special scientific importance. Each planet or moon should have as few names as possible, and names should not be repeated on different bodies unless it makes sense. Names should be in their original language, and themes from early space naming are used when possible. The rules also make sure names are fair and from many different cultures, and they avoid names that are political, military, or religious, except for very old figures. Only people who have been gone for at least three years can have features named after them.

Naming conventions

When we give names to features on planets and moons, we follow special rules so everyone knows exactly what we’re talking about. For most features, we add a certain word to the name — like calling a big flat area a “planitia.” But for some places, like craters, the name alone is enough. On places like Io and Triton, some features change quickly and don’t need that extra word.

These naming rules stay the same for big or small features, except for valleys and craters on Mars and Venus, where the rules change depending on size. Some names, like “regio,” were used a long time ago to describe big areas on the Moon and Mercury when we could only see them through telescopes. Today, we still use them for large regions.

For very small worlds where we don’t yet know exact locations, names are shown on special drawings made when the names were picked. Rings around planets and gaps in those rings are named after scientists who studied them. Right now, names for features in planet atmospheres are just temporary, and we’ll pick a permanent system later.

Sometimes during space missions, scientists give quick, easy names to small spots like landing sites or tiny hills. These aren’t official names yet, but if they become official, they’ll still follow the same rules as the bigger names.

Descriptor terms (feature types)

Astronomers have named different kinds of features on planets and moons, such as craters, mountains, and valleys, to help describe and locate them. These names make it easier for scientists and space explorers to talk about specific spots on these worlds.

The International Astronomical Union (IAU) was created in 1919 to decide on and standardize these names, ensuring everyone uses the same terms when discussing features on bodies in our Solar System like the Moon and Mars.

Categories for naming features on planets and satellites

Mercury

Features on Mercury are named based on famous artists, musicians, authors, and composers who have died before the year 1950. This helps honor their contributions to culture and history.

Venus

Almost all features on Venus are named after women from history and mythology, such as goddesses and famous women. Three features have different names because they were named before this rule was made. These are Alpha Regio, Beta Regio, and Maxwell Montes, which is named after James Clerk Maxwell.

The Moon

Features on the Moon have special names that help scientists and explorers talk about them clearly. There are lists of features, craters, seas (called maria), mountains, and valleys on the Moon that help us learn more about our closest neighbor in space.

Mars and martian satellites

Mars

When robots land on Mars, they sometimes give funny names to small features like rocks or sand dunes. Some of these names come from ice cream flavors, cartoon characters, or famous music groups from the past.

Deimos

Features on Deimos, one of Mars's small moons, are named after writers who wrote stories about Martian moons. The two named features are Swift crater and Voltaire crater, named after Jonathan Swift and Voltaire, who guessed that Mars might have moons long before we could see them.

Phobos

All features on Phobos, the other moon of Mars, are named after scientists who studied Mars's moons or after characters and places from Jonathan Swift's book Gulliver's Travels.

Satellites of Jupiter

Amalthea

Features on Amalthea are named after people and places from stories about Amalthea, a mythical nurse of the baby Zeus.

Thebe

The only feature on Thebe is named after people and places from stories about Thebe.

Io

Io, one of Jupiter's moons, has many named features that scientists study. There are lists of its mountains and special flat areas called paterae.

Europa

Europa also has lists of its features, craters, and lineae (long cracks or ridges).

Ganymede

Ganymede, the largest moon of Jupiter, has its own lists of named features for scientists to study.

Callisto

Callisto also has lists of its features and craters to help scientists understand its surface.

Satellites of Saturn

Janus

Features on Janus are named after characters from stories about the twins Castor and Pollux.

Epimetheus

Like Janus, Epimetheus also has features named after characters from the same twins' stories.

Mimas

Features on Mimas are named after people and places from old stories in Le Morte d'Arthur, a famous book about King Arthur.

Enceladus

Enceladus's features come from stories in Arabian Nights, a collection of folktales.

Tethys

Tethys's features are named after people and places from Homer's Odyssey, an ancient story about adventures at sea.

Dione

Features on Dione are named after characters from Roman myths or from Aeneid, a famous poem by Virgil.

Rhea

Rhea's features come from myths about creation and the beginnings of the world.

Titan

Titan, Saturn's largest moon, also has lists of its named features for scientists.

Hyperion

Features on Hyperion are named after gods of the Sun and Moon.

Iapetus

Iapetus's features are mostly named after characters from old French poems, except for Cassini Regio, named after its discoverer, Giovanni Cassini.

Phoebe

Phoebe has its own sets of named features.

Satellites of Uranus

Moons of Uranus are named after characters from plays by William Shakespeare or from The Rape of the Lock.

Puck

Features on Puck are named after mischievous spirits, just like the character Puck from Shakespeare.

Miranda

Miranda’s features are named after male characters and places from Shakespeare's plays.

Ariel

Ariel’s features are named after light spirits.

Umbriel

Umbriel’s features are named after dark spirits.

Titania

Titania’s features are named after female characters and places from Shakespeare.

Oberon

Oberon’s features are named after tragic heroes and places from Shakespeare.

Small satellites

Eventually, features on Uranus's smaller moons will be named after heroines from Shakespeare's plays and poems by Pope.

Satellites of Neptune

Proteus

Features on Proteus are named after water spirits, gods, or goddesses who are not from Greek or Roman stories. The only named feature is the crater Pharos.

Triton

Triton's features are given aquatic names, avoiding those from Roman and Greek origins. These can include names of spirits, fountains, geysers, or islands.

Nereid

Nereid currently has no named features, but when they are found, they will be named after nereids—water spirits from myths.

Small satellites

Features on Neptune's smaller moons will be named after gods and goddesses from myths about Neptune/Poseidon or other water-related beings.

Pluto and satellites

In February 2017, the IAU approved special themes for naming features on Pluto and its moons.

Pluto

Main articles: Geography of Pluto and List of geological features on Pluto

Features on Pluto can be named after gods and goddesses from underworld stories, heroes who explored unknown places, scientists who studied Pluto, and pioneers in space travel.

Charon

Main articles: Geography of Charon and List of geological features on Charon

Charon's features are named after places and journeys from space stories, fictional explorers, and artists who inspired space adventures.

Nix

Features on Nix are named after deities of the night.

Hydra

Hydra's features are named after legendary serpents and dragons.

Kerberos

Kerberos's features are named after dogs from stories and history.

Styx

Styx's features are named after river gods.

Asteroids

1 Ceres

See also: List of geological features on Ceres

4 Vesta

See also: List of geological features on Vesta

243 Ida

See also: List of geological features on 243 Ida and Dactyl

(243) Ida I Dactyl

951 Gaspra

See also: List of geological features on 951 Gaspra

253 Mathilde

See also: List of craters on 253 Mathilde

433 Eros

See also: List of geological features on 433 Eros

25143 Itokawa

See also: List of geological features on 25143 Itokawa