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Xena Awarded Dwarf Planet Status
by Staff Writers
Pasadena CA (SPX) Aug 25, 2006

The International Astronomical Union (IAU) today downgraded the status of Pluto to that of a "dwarf planet," a designation that will also be applied to the spherical body discovered last year by California Institute of Technology planetary scientist Mike Brown and his colleagues... The ruling effectively settles a year-long controversy about whether the spherical body announced last year and informally named "Xena" would rise to planetary status.

Though somewhat larger than Pluto, the body has been informally known as "Xena" since the formal announcement of its discovery on July 29, 2005 by Brown and his co-discoverers, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University. Xena will now be known as the largest dwarf planet. "I'm of course disappointed that Xena will not be the tenth planet, but I definitely support the IAU in this difficult and courageous decision," said Brown. "It is scientifically the right thing to do, and is a great step forward in astronomy.

Xena was discovered on January 8, 2005, at Palomar Observatory with the NASA-funded 48-inch Samuel Oschin Telescope. Xena is about 2,400 kilometers in diameter. A Kuiper-belt object like Pluto, but slightly less reddish-yellow, Xena is currently visible in the constellation Cetus to anyone with a top-quality amateur telescope. Brown and his colleagues in late September announced that Xena has at least one moon. This body has been nicknamed Gabriella after Xena's sidekick on the television series.

Xena is currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), which means that it is some nine billion miles away at present. Xena is on a highly elliptical 560-year orbit, sweeping in as close to the sun as 38 astronomical units. Currently, however, it is nearly as far away as it ever gets. However, Pluto's own elliptical orbit takes it as far away as 50 astronomical units from the sun during its 250-year trip around the sun. This means that Xena is sometimes much closer to Earth than Pluto-although never closer than Neptune.

Gabrielle is about 250 kilometers in diameter and reflects only about 1 percent of the sunlight that its parent reflects. Because of its small size, Gabrielle may very well be oddly shaped. [Sorry, I couldn't suppress a snort of laughter at that one, as someone who found Gabrielle - mis-spelled as Gabriella in the original article, and corrected here - one of the most immensely irritating things about Xena: Warrior Princess. The whole subtext thing, and the obsession over it in certain fandom circles, came perilously close to derailing my liking for the show entirely]

Brown says that the study of Gabrielle's orbit around Xena hasn't yet been fully determined. But once it is, the researchers will be able to derive the mass of Xena itself. That's because the entire mass of the system - Xena and Gabrielle - orbits a common center of gravity. Therefore, once the researchers figure out the distance between the moon and its parent, how fast the moon revolves its parent, and how much the moon makes Xena wobble, then they'll know how much Xena weighs. And this information will lead to new insights on its composition.

Based on spectral data, the researchers think Xena is covered with a layer of methane that has seeped from the interior and frozen on the surface, As in the case of Pluto, the methane has undergone chemical transformations, probably due to the faint solar radiation, that has caused the methane layer to redden. But the methane surface on Xena is somewhat more yellowish than the reddish-yellow surface of Pluto, perhaps because Xena is farther from the sun. Brown and Trujillo first photographed Xena with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of 2005.

Source: Space Daily, August 25, 2006

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