All Hail Eris and Dysnomia

2003 UB313
Michael Brown (Caltech) and his team discovered 2003 UB313's moon in this image shot at Keck Observatory in Hawaii.

Remember 2003 UB313, the body often called by its nickname, Xena? On July 29, 2005, when Michael E. Brown (Caltech) announced his team's discovery of the distant Kuiper Belt object (KBO), it sent shock waves through the planetary-science community. Some 75 years after Clyde Tombaugh discovered Pluto, astronomers had at long last found an object larger than the "ninth planet." But what to call it? Was it a planet? A KBO? Something else? For more than a year the distant, icy body went by a nine-syllable jargony moniker, or by a nickname that came from a campy television show that starred a warrior princess. According to International Astronomical Union (IAU) guidelines, how an object is named depends entirely on how the object is classified. Planets are named for Roman gods, and classical KBOs are named for creation gods. But scattered-disk objects (bodies whose orbits are steeply inclined to the plane of the solar system) don't have naming conventions. So as long as 2003 UB313 might possibly earn planet status, it was stuck in naming purgatory.

After much debate, infighting, animosity, and angst, last month the IAU finally made its decision and decreed that the solar system has just eight planets. The now-former planet Pluto and 2003 UB313 were both dubbed "dwarf planets." And with the definitions set, yesterday the IAU announced the unnamed dwarf planet's new title.

According to the IAU Committee on Small-Body Nomenclature and the
Working Group on Planetary-System Nomenclature, 2003 UB313 will now go by the name Eris (pronounced EE-riss). "The name is fitting," says Brown. Eris is the Greek goddess of strife and discord. As the story goes, Eris caused wars by creating infighting among others. Given the turmoil within the astronomical community surrounding Eris's classification, its name carries a much deeper, political meaning indeed.

But there's more to the name. "We were sad that Xena went away," says Brown, so the team held onto her in subtle ways — through the name of Eris's moon.

The satellite, now called Dysnomia (pronounced diss-NOH-mee-uh), is named for Eris's daughter, the goddess of lawlessness — a tribute, says Brown, to the actress who played Xena, Warrior Princess: Lucy Lawless. But Brown is quick to point out that the moon also follows another tradition for "dwarf planet" satellite names: Pluto's moon Charon was discovered in 1978 by James W. Christy, and the first syllable in Charon matches the first syllable in Christy's wife's name, Charlene. Brown's wife's name is Diane. "We're going to call the moon Di," says Brown.

The IAU sub-committees voted nearly unanimously in favor of the two names (as reported in IAU Circular 8747), and the IAU Executive Committee approved the decision.

COMMENT