Naming The Planets, Part II

A question to the discussion forum a week or so ago asked about the origins of the names of the planets. The "official" names of objects in the solar system are assigned by the International Astronomical Union (IAU), a global association of astronomers. The IAU follows several conventions in naming planets and moons, the main ones being that planets are given names of Roman mythological beings and moons are given Greek mythological names associated with the Greek equivalent of the Roman god. Many of these names did not originate with the IAU, but have borne the names of these deities dating back into antiquity. There are exceptions to the IAU naming conventions. Shakespearean names are assigned to moons of Uranus and the occasional Norse or Inuit mythological name appears here and there.

Here is the second half of our examination of the names of the planets and moons.

Saturn, the sixth planet from the sun and the second largest, is named after the king of the Titans, the father of Jupiter. Saturn’s Greek counterpart is Cronos. English use of Saturn as the planetary name dates back to Old English. The adjective is Saturnian, 1557.

Like Jupiter, Saturn has many satellites. The Saturnian moons tend to be named after Titans from myth, although there are many exceptions:

  • Pan, named after the Greek god of nature. Discovered by astronomer Mark Showalter in 1990 from Voyager photos.
  • Atlas, after the Titan condemned to support the heavens on his shoulders. Discovered by Richard Terrile in 1980 from Voyager photos
  • Prometheus, Greek for foresight, after the Titan who gave fire to man. Discovered by S. Collins in 1980 from Voyager photos
  • Pandora, after the first woman in Greek mythology. Discovered by Collins in 1980 from Voyager photos.
  • Epimetheus, Greek for hindsight, brother of Prometheus. This moon was first observed by Walker in 1966, but was confused with Janus (see next). In 1977, Fountain and Larson demonstrated they were separate objects.
  • Janus, after the Roman god of doorways. Discovered by either Walker or Audoin Dolfus in 1966. Dolfus sighted it a few hours before Walker, but it is uncertain whether Dolfus saw Janus or Epimetheus
  • Mimas, after a Titan slain by Hercules. Discovered by William Herschel in 1789.
  • Enceladas, after a Titan slain by Athena. Discovered by Herschel in 1789
  • Tethys, after a Titaness and sea goddess. First seen by Giovanni Cassini in 1684.
  • Telesto, after the daughter of Tethys. Discovered by Smith, Reitsma, Larson and Fountain in 1980.
  • Calypso, after the sea nymph who delayed Odysseus for seven years. Discovered by Pascu, Seidelmann, Baum, and Currie in 1980
  • Dione, after the mother of Aphrodite. Spotted by Cassini in 1684
  • Rhea, after the sister and wife of Cronus, the mother of Zeus. Discovered by Cassini in 1672.
  • Titan, the largest of the Saturnian satellites, is named after the family of giants overthrown by Zeus. Christiaan Huygens discovered this moon in 1655.
  • Hyperion, after a Titan. Discovered by William Bond and William Lassell in 1848.
  • Iapetus, a Titan, the father of Prometheus and Atlas. Discovered by Cassini in 1671.
  • Phoebe, after the daughter of Uranus and Gaia. Discovered by William Pickering in 1898.
  • Several Saturnian moons, discovered in 2000, were given names by IAU in 2004, Norse, Gallic, and Inuit names represent satellites in three different inclination groups
    • Ymir, Norse giant
    • Paaliaq, Inuit giant
    • Tarvos, Gallic giant
    • Ijiraq, Inuit giant
    • Suttungr, Norse giant
    • Kiviuq, Inuit giant
    • Mundilfari, Norse giant
    • Albiorix, Gallic giant
    • Skathi, Norse giantess
    • Erriapo, Gallic giant
    • Siarnaq, Inuit giant
    • Thrymr, Norse giant

Uranus, named after the Greek deity of the heavens, husband of Gaia and father of Cronus, is the seventh planet and the first to be discovered in modern times. It was first sighted by Herschel in 1781. Herschel named it the Georgium sidus (the Georgian planet) in honor of King George III. The name Uranus was proposed by Johann Bode sometime before 1802. The adjective is Uranian, 1844.

Uranian moons follow a different naming convention than most objects in the solar system. Instead of being named after characters in Greco-Roman myth, they are named after Shakespearian characters:

  • Cordelia, after King Lear’s daughter. Discovered by Voyager 2 in 1986.
  • Ophelia, after Polonius’ daughter from Hamlet. Discovered by Voyager 2 in 1986.
  • Bianca, after Katherine’s sister in The Taming of the Shrew. Discovered by Voyager 2 in 1986.
  • Cressida, after the title character in Troilus and Cressida. Discovered by Voyager 2 in 1986.
  • Desdemona, after Othello’s wife. Discovered by Voyager 2 in 1986.
  • Juliet, after the heroine of Romeo and Juliet. Discovered by Voyager 2 in 1986.
  • Portia, after a character in Merchant of Venice. Discovered by Voyager 2 in 1986.
  • Rosalind, after a character in As You Like It. Discovered by Voyager 2 in 1986.
  • Belinda, taking a break from the Bard, this moon is named after a character in Pope’s The Rape of the Lock. Discovered by Voyager 2 in 1986.
  • Puck, after the fairy in A Midsummer Night’s Dream. Discovered by Voyager 2 in 1986.
  • Miranda is the innermost of the Uranian large moons and is named after a character in The Tempest. Discovered by Gerard Kuiper in 1948.
  • Ariel, named after a spirit in The Tempest, was discovered by William Lassell in 1851.
  • Umbriel is another Uranian moon that is not named after a Shakespearian character. Again, the name is from The Rape of the Lock. Discovered by Lassell in 1851.
  • Titania was queen of the fairies in A Midsummer Night’s Dream. It was discovered by Herschel in 1787.
  • Oberon, was king of the fairies and husband to Titania. It was also discovered by Herschel in 1787.
  • Caliban, Sycorax, Trinculo, Prospero, Setebos, and Stephano, were all discovered in the late 1990s and named after characters in The Tempest.
  • Several other moons of Uranus have been discovered, but have yet to be named.

The eighth, and some would say last, planet is Neptune, named for the Roman god of the sea. It was discovered by Johann Galle and Heinrich d’Arrest in 1846, although Galileo had seen in 1613, but mistook it for a star. Due to Pluto’s highly eccentric orbit, Neptune is sometimes the outermost planet. The adjective is Neptunian, 1849.

As one might expect for a planet named after the god of the sea, Neptunian moons all have a watery flavor to their names:

  • Naiad, named after type of water nymph, was discovered in 1989 by Voyager 2.
  • Thalassa, named after the Greek personification of the sea, another name for Tethys (see Saturnian moons), was also discovered in 1989 by Voyager 2.
  • Despina, a third moon found in 1989 by Voyager 2, is named after a nymph, the daughter of Poseidon, 1989 by Voyager 2.
  • Galatea is named for the daughter of the cyclops Polyphemus, a granddaughter of Poseidon, not after the statue of the same name carved by Pygmalian that came to life. It, too, was discovered in 1989 by Voyager 2.
  • Larissa, is named after the daughter of Pelasgus. No specific myths connected with her. It is yet another Voyager 2 moon.
  • Proteus, is named after the shape-changing sea-god, the sixth and last moon discovered by Voyager 2 in 1989.
  • Triton, is the only large moon of Neptune. It is named after a god of the sea, the son of Poseidon. It was discovered in 1846 by Lassell.
  • Nereid, the name for the fifty daughters of the Titan Nereus, was found in 1949 by Kuiper.

Pluto was discovered in 1930 by Clyde Tombaugh and named after the Roman god of the underworld. Astronomers are currently debating whether Pluto should be classified as a planet because of its small size and its orbit that is inclined outside the plane of the other planets. Pluto has three moons, one named. Charon, discovered in 1978 by Jim Christy, is named after the ferryman who takes departed souls over the river Acheron into Hades

The recently discovered Sedna is so far out, more than twice as far from the sun as Pluto, that its orbital period is 10,500 years. Slightly smaller than Pluto, Sedna was discovered in 2004 and named after the Inuit goddess of the sea. Given the controversy over Pluto’s planetary status, it is unlikely that Sedna will be classified as a planet.

In June of this year, astronomers Mike Brown, Chad Trujillo, and David Rabinowitz announced the discovery of the tenth planet. The planet currently has a designation of 2003 UB313. A permanent name has been proposed and is under review by the IAU, but what that is and whether the IAU will accept it is unknown. Little is known about 2003 UB313, although it is definitely bigger than Pluto—the best guess puts it at about 125% of Pluto’s size or somewhat larger than Triton. 2003 UB313 orbits the sun at a distance of 97 astronomical units, making it the most distant object known to orbit the sun. (Earth orbits at one astronomical unit; Pluto is at about 40, and Sedna is at 90.) In September, a moon orbiting 2003 UB313 was found.

Hypothetical Objects

Over the years, the existence of various objects in the solar system have been postulated but never found to actually exist. Here are some that went so far as to have (unsanctioned by the IAU) names.

Vulcan was the name of a planet believed, based on perturbations in Mercury’s orbit, to orbit between the sun and Mercury. It was named by Urbain Le Verrier in 1859 after the Roman blacksmith god. In 1916, Einstein’s General Theory of Relativity explained Mercury’s orbital oddities without need for Vulcan to exist. In 1970-71, the belief in Vulcan was temporarily revived when astronomers observed some faint objects within Mercury’s orbit, but these turned out to be comets passing close by or striking the sun.

Neith is a supposed moon of Venus. It was first "sighted" by Cassini in 1672. It was "seen" by several astronomers between that year and 1892. Controversial because not all who looked for it saw it, Neith is now known not to exist and the "sightings" were confusions with stars and other objects. Neith was the Egyptian goddess of war and the hunt.

Themis is a supposed moon of Saturn. "Sighted" by Pickering in 1905, it remained in some almanacs into the 1960s. Themis was a Titan, the mother of the three Fates.

Nemesis is a faint star believed by some to be the Sun’s binary companion at a distance of about 1.4 light years. According to those who believe in its existence, every 30 million years Nemesis comes close enough to disturb the Oort cloud, sending a shower of comets into the inner solar system and causing impacts on Earth and the other planets. The alleged star was named in 1984 after the Greek goddess of retribution. No firm evidence for the existence of Nemesis has ever been presented and its existence is highly doubtful.

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