How do astronomers decide what to call celestial objects near our Solar System?



  1. 0 Votes

    Solar System

    How do astronomers go about naming celestial bodies?

    Think about the planets in the solar system besides Earth.

    Mercury… Venus… Mars…

    Jupiter… Saturn…

    Uranus… Neptune…

    What’s a common factor there?

    Their names.

    All seven of the non-Earth planets have names that are derived from the names of Roman gods. (Uranus is a special case – its name is the Greek variant of a Roman god.) Mercury, the messenger god; Venus, the goddess of love; Mars, the god of war; Jupiter, king of the gods; Saturn, Zeus’ Titan father; Uranus, god of the sky; and Neptune, god of the ocean.  

    The question then becomes: if we have named our planets after Roman gods, what are the origins of the names of other types of celestial bodies?

    Our solar system’s planets and their satellites

    Many of the planets of the solar system have been traditionally bright enough for ancient peoples to see in the night sky. As such (and as explained above), they have names derived from those of Roman gods. Uranus and Neptune were both discovered much later – 1781 and 1846, respectively. To match tradition and precedent, these two were also given godly names.

    The Earth’s moon has always been called some variant of the English word “moon”; for example, the French call it Lune, and the Romans called it Luna.  

    In 1877, Asaph Hall discovered Mars’ two moons, naming them after either horses that drew Mars’ chariot, or two of Mars’ “attendants” (depending upon the source). These are Phobos (the innermost moon) and Deimos (its outer brother).

    Jupiter’s moons, which make up the Jovian system, take after their planet. They are all named for mythological figures who were Jupiter’s “lovers and descendants”. Take Io, who Jupiter famously transformed into a cow to shield her from Hera. Or Europa, who Jupiter ensnared while in the form of a white bull.

    With the exception of Janus (which is named after the two-faced Roman god of the beginning), moons in the Saturnian systems have names just short of godliness. In particular, they’re named after titans, the titans’ descendants, and mythological giants. One example is Rhea, Saturn’s wife and Jupiter’s father. Another is Helene (“Helen”), a fatally beautiful granddaughter of Saturn.

    Uranian satellites abandon this dependence upon Greco-Roman mythology. Instead, the discoverers of these moons turned to literature. These moons are all named after either Shakespearean characters (Miranda; Cordelia; Ophelia) or poet Alexander Pope’s 1712 “The Rape of the Lock” (Ariel; Umbria; Titania).

    With Neptune, however, planetary and satellite discoverers returned to the mythological tradition. Neptune’s moons are related to either Neptune himself (Despina) or the oceans that were his domain (Proteus). “Irregular” moons (e.g. Galatea) receive special distinction: they are named after Neptune’s attendants.

    Dwarf planets and their respective systems

    It should be noted that the discoverers of our solar system’s dwarf planets stuck to planetary precedent: they named these celestial bodies after mythological gods. Ceres, Pluto and Eris are all named after Greco-Roman deified figures, while Haumea and Makemake both represent the traditions of Hawaiian mythology. 


    The asteroids of the Asteroid Belt have varied names. Some, like the planets that lie adjacent to them, have mythological names: Eros; Ida; Linus. Others are tributes: to France’s “Little Prince”, or to a Parisian astronomer’s wife. And one – Gaspra – is named for a resort on the Crimean. Not quite “mythological”, that one…

    Minor Planets

    The process of naming a minor planet is more procedural than traditional. The discoverer of a minor planet gets to submit his or her choice of name to the IAU’s Working Group for Small Body Nomenclature. He or she must both explain the choice and ensure that it fits within IAU’s guidelines; for example, the name of a minor planet cannot exceed sixteen characters, and “names of pet animals are discouraged”. (I’ve placed an example of a minor planet name in the Sources.)

    There are some examples, though, where tradition takes precedent:

    — If an asteroid is “Trojan” (that is, its orbit has a 1:1 resonance with Jupiter), it receives the name of a Trojan war hero.

    — If an object crosses or approaches Neptune’s orbit but has a resonance other than 1:1, it receives the name of a mythological character with connections to the underworld.

    — If an object crosses or approaches Earth’s orbit, it receives the name of some mythological figure.

    — If a planet crosses or approaches the orbit of a giant planet (e.g. Jupiter, Saturn) but does not do so in a stabilizing resonance, it receives the name of a mythological centaur.

    — If an object is outside Neptune’s orbit by a very, very large margin, it receives the name of a mythological character with connections to creation.


    Comets are conventionally named after their discoverers. This convention was established in the early twentieth century.




  2. 0 Votes

    Minor planets are named based on the year of discovery, two letters, and more numbers if needed. Once the orbit of the minor planet is determined and a location can be estimated, it is assigned a permanent number.

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