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Planetary News: Trans-Neptunian Objects (2006)

Eris, Goddess of Strife, Joins Solar System Amid Raucous Debate

By Amir Alexander
14 September, 2006

2003 UB313, the giant Kuiper belt object (KBO) whose discovery shook the entire solar system, now has an official name. On September 13, 2006, the International Astronomical Union's (IAU) working groups on planetary system nomenclature and small body nomenclature voted almost unanimously to accept the suggestion of the objects' discoverers and name it Eris, after the Greek goddess of discord and strife.

Eris is the largest object detected in the solar system since the discovery of Neptune in 1846. When it was announced to the world by its discoverers Michael Brown of Caltech, David Rabinowitz of Yale, and Chad Trujillo of the Gemini Observatory in 2005, it caused a crisis of definitions in the astronomical community, as well as in the general public. The reason? It was bigger than Pluto, the smallest of the nine traditional planets.

The common understanding of the term "planet" had already been under scrutiny in recent years due to the discovery of other giant KBOs, which were nearly as large as Pluto, and the detection of giant planets outside the solar system. But it was the discovery of Eris, or 2003 UB313 as it was known at the time, which brought the question to a head. If Pluto is a planet, then surely the larger Eris should be a planet, and quite likely the other giant KBOs as well; but if Eris is not a planet, then Pluto shouldn't be one either. One thing was clear: it was time to decide. The debate led directly to the IAU's decision on August 24 to strip Pluto of its planetary status and establish a new category of "dwarf planets" that includes Pluto, Eris, and similar large objects on the periphery of the solar system. Nevertheless, despite the IAU's vote, the uproar continues and shows no sign of dying down.

Artist's depiction of Eris and its moon, Dysnomia
Click to enlarge >
Artist's depiction of Eris and its moon, Dysnomia
Credit: Robert Hurt (IPAC)

This background, according to discoverer Michael Brown, makes the name assigned to the new object entirely appropriate. "The Goddess Eris," said Brown, "created all sorts of problems by causing people to quarrel among themselves. That's exactly what the dwarf planet Eris did as well." Explaining why he and his collaborators had proposed the name to the IAU in the first place, he said simply: "it was just too perfect to pass up."

Eris's moon, formerly known by the catchy designation S/2005 (2003 UB313) 1, was also given a name – Dysnomia, who in Greek mythology is Eris's daughter and the Daimon spirit of lawlessness. In addition to the implicit reference to the ongoing controversy, Dysnomia's name is also a nod towards the unofficial nickname by which 2003 UB313 had been known until now – "Xena," the warrior princess of television fame. "Although Xena is now gone from the sky," explained Brown, "we wanted her fans to know that the spirit of Lucy Lawless is still out there." Lucy Lawless is the actress who played Xena on television.

Whether it be called a planet, dwarf planet, KBO, or something else entirely, the solar system now has a new member whose name reflects the uncertainty and confusion it brought with it. Perhaps by joining together to name the newcomer, planetary scientists have taken a first step towards bringing the field back under the sway of Dysnomia's counterpart, Eunomia – the goddess of good order.