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Largest Dwarf Planet Given Name Eris

September 13, 2006

The dwarf planet 2003 UB313, which sparked the recent demotion of Pluto to a dwarf planet, was formally given the name Eris on this day by the International Astronomical Union (IAU). Its moon was given the name Dysnomic.

The new names come from Greek mythology. Eris is the Greek goddess of strife; “strife” is the literal translation of her Greek name. Depending on which poet you read, she is either the daughter of the night (Hesoid) or the sister of Ares (Homer), the Greek god of war. Among her many daughters is Dysnomic, which means lawlessness in Greek.

Eris sparked the discord among the goddesses Hera, Athena, and Aphrodite that led to the Trojan War by tossing the Apple of Discord, a golden apple inscribed with “For the most beautiful one,” into their midst. When Paris, the prince of Troy, was chosen to select the most beautiful of these three goddesses, he selected Aphrodite after she promised him Helen, the wife of Menelaus of Sparta. Helen's abduction drew the Acheans to Troy, which they besieged and destroyed.

Inspiration for giving Eris its name clearly came from the fight over whether dwarf planets such as Eris, Pluto, and Ceres (in the asteroid belt between Mars and Jupiter) should be considered on the same level as the planets Mercury and Mars, revealing a contentiousness among astronomers over the new planetary terminology that was not obvious in the press releases and news reports.

Eris is the largest of the known Kuiper belt objects, with a diameter that is 5% larger than that of Pluto. It is the most distant of the known dwarf and classical planets, with an aphelion of 97 AU, compared to an aphelion of 50 AU for Pluto and of 30 AU for Neptune. The orbit is highly eccentric, having a perihelion of 38 AU. Little is known about its moon Dysnomic other than its size relative to Eris is likely similar to the size of the Moon relative to Earth.

There's no information of what inspired the IAU to name Dysnomic as they did, other than that she is the daughter of Eris. But one can't help notice that Xena, the old nickname for the dwarf planet Eris, is a television character played by the actress Lucy Lawless. Coincidence?

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