StarChild Question of the Month for August 2002


How do planets and their moons get their names?



The official names of planets and their moons are governed by an organization called the International Astronomical Union (IAU). The IAU was established in 1919. Its mission is "to promote and safeguard the science of astronomy in all its aspects through international cooperation". Its individual members are professional astronomers from all over the World. The IAU is the internationally recognized authority for assigning names to celestial bodies and any surface features on them.

The IAU recognizes that astronomy is an old science and many of its names come from long-standing traditions and/or are founded in history. For many of the names of the objects in the solar system, this is especially so. Most of the objects in our solar system received names long ago based on Greek or Roman mythology. The IAU has therefore adopted this tradition in its rules for naming certain types of objects in the solar system.


With the exception of Earth, all of the planets in our solar system have names from Greek or Roman mythology. This tradition was continued when Uranus, Neptune, and Pluto were discovered in more modern times.

Natural Satellites

For those moons have been known for a long time (such as the Galilean moons of Jupiter), the names were assigned from mythological characters. For example, the moons of Jupiter were named for characters who had roles in the life of Zeus (the Greek mythology counterpart of the Roman God Jupiter).

For recently discovered natural satellites of the planets, they are first given a "provisional" or temporary name while additional observations are made to confirm their existence. This temporary name (usually consisting of the year of discovery and some number indicating the order of discovery in that year) is assigned by an organization called the Central Bureau for Astronomical Telegrams (CBAT). For example, when Voyager 2 found a bunch of new moons in its 1989 Neptune encounter, they were named S/1989 N 1, S/1989 N 2, etc. When the existence of the object is confirmed (and its orbit determined), it is given a final name. The name is suggested by the discoverer(s), but following tradition is strongly encouraged.

Note that the moons of Uranus are a special case in our solar system. They are named after literary characters (from works by William Shakespeare and Alexander Pope) rather then characters from mythology.

Surface Features

Landscape features on planets and natural satellites follow a set of complicated conventions set by the IAU Nomenclature Committee. The rules set restrictions on allowable names such as: a planetary feature may not bear the name of a living person or of a political or religious figure from the last 200 years.

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