Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
Early observers thought the dark plains on the Moon were seas and lakes and gave them names like Mare Tranquillitatis (Sea of Tranquillity, where Apollo 11 landed). We retain those traditional names even though, of course, we know they are not seas. (The terms Lacus, "lake" and Mare, "sea" have now been applied to true bodies of liquid on Titan.)
In the 1600's, the Italian astronomer Giovanni Riccioli began the custom of naming craters on the Moon for great astronomers. A large crater was later named for Riccioli himself. There's almost a perverse, inverse relationship between the size of a crater and the astronomer's contribution to lunar studies. Great as Plato, Tycho, and Copernicus are, they did not advance our understanding of the Moon much, but they have some of the largest and most conspicuous craters named for them. (By the time telescopes were powerful enough to allow serious research on the Moon, all the good craters were taken!)
Planetary probes revealed that there are far more craters than astronomers, great and otherwise, so names of objects on other planets are derived from other biographical categories or mythology. A commission of the International Astronomical Union oversees naming, and the names (so far) are recognized by the various spacefaring nations. The rules are:
Planetary geographical features have Latin names. Latin is traditional, apolitical, and the closest thing to a universal language in history. The following are in use, with the literal Latin translation in parentheses, followed by the geographical meaning.
Australis, Meridionalis - South
Borealis, Septentrionalis - North
The U.S. Geological Survey site, Gazetteer of Planetary Nomenclature, gives a complete listing of naming conventions. The main themes are listed here.
Inventor of the lyre in Greek mythology, hence craters named for great figures in the arts. Large regions are named for deities equivalent to Mercury.
Female figures in history and mythology
Some traditional names were given by Earth-based observers and are preserved, sometimes with appropriate modifications. For example, the white spot Nix Olympica (the snows of Olympus) is now known to have been a cloud cap over the volcano Olympus Mons. Some large craters were named early on for famous scientists. Small craters named for cities and towns on Earth.
The moons of Jupiter presented astronomers with a brand new problem. They were the first completely new objects ever discovered in the Solar System. Galileo, who knew a marketing opportunity when he saw one, wanted to name them The Medicean Stars, after the powerful Medici family that ruled Florence, and who would presumably support Galileo handsomely. German astronomer Simon Marius proposed the names we now use.
The names should obviously be connected to Jupiter, yet subordinate. If you're familiar with mythology, you realize this definitely rules out Hera, or Juno, Jupiter's jealous wife (anyway, a large asteroid bears the name Juno). Her main hobby was breaking up Jupiter's innumerable love affairs and inflicting vengeance on the lovers. So satellites of Jupiter are named for figures with whom Jupiter had love affairs. Jupiter worked industriously to keep astronomers well supplied with names for satellites. However, not even Zeus was able to keep up with the tally of satellites (he tried!) and newly discovered satellites may also be named for offspring of Zeus and other mythological figures.
Incidentally, Ganymede was a boy. The Greeks were fairly tolerant of such things. The four largest satellites and the naming conventions used on each are:
Uranus is the only body in the Solar System with moons not named from classical mythology - its moons are named from works by Shakespeare and Alexander Pope. Any future satellites will follow that naming convention.
Neptune, god of the sea, has satellites named for minor deities connected with sea myths. Features on Triton have aquatic names.
Features on Pluto will be drawn from underworld myths.
Names of minor planets rapidly ran out of mythological characters and now include cities, observatories, people (the dead Challenger and Columbia astronauts among them) and many other things. The minor planets with named features typically follow some theme associated with the name of the minor planet itself. 951 Gaspra, named after a European spa, has craters named after spas, and so on. Having some class of features named after people involved in mapping the body is also common. 433 Eros, named after the Greek god of love, will have craters named after famous erotic figures. Before you nominate yourself, bear in mind that features cannot be named after living people.
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Created 20 May 1997, Last Update 1 November 1999