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A new planet and other strangers (“Santa,” “Easterbunny,” and “Xena.”)

http://pr.caltech.edu/periodicals/336/articles/Volume%205/09-22-05/planet.html

Caltech professor of planetary astron-omy Mike Brown and his colleagues announced a startling discovery on July 29: a new planet larger than Pluto in our solar system. But they also found two other objects, and all three are oddities that could revolutionize our understanding of the solar system.

The discoverers have nicknamed the objects “Santa,” “Easterbunny,” and “Xena.” Brown, along with former Caltech postdoc Chad Trujillo, who is currently at the Gemini Observatory in Hawaii, and David Rabinowitz of Yale, detected the three objects with the 48-inch Samuel Oschin Telescope at Palomar Observatory.

All three objects are nearly Pluto-sized or larger, with Xena large enough to be called the tenth planet. The three also have odd elliptical orbits, and are members of the Kuiper belt, a region beyond Neptune’s orbit that for decades was merely theoretical. When astronomers began detecting Kuiper-belt objects in the mid-1990s, the region suddenly became reality.

Xena, which is currently about 97 astronomical units away (one AU equals the distance between the sun and Earth, or approximately 93 million miles), is at least the size of Pluto and probably much larger. The researchers hope that infrared data returned by the Spitzer Space Telescope in late August, plus recent data from the 30-meter IRAM telescope in Spain, will help nail down Xena’s size. Brown predicts that Xena will be highly reflective, because spectrographic data gathered by Trujillo show the surface composition is similar to that of Pluto. If, like Pluto, Xena reflects 70 percent of the sunlight reaching it, then it is about 2,700 kilometers (over 1,600 miles) in diameter.

The second object, nicknamed Santa because it was found on December 28, 2004, is one of the more bizarre objects in the solar system, according to Rabinowitz. His observations from a small telescope in Chile show that Santa is a cigar-shaped body whose length is about the diameter of Pluto. No large body in the solar system comes close to rotating as fast as Santa, which has a four-hour period. Observations by the team at the W. M. Keck Observatory have shown that Santa also has a tiny moon, nicknamed Rudolph, which circles it every 49 days.

Easterbunny, so named because of its discovery last March, is 52 astronomical units away, and like Santa is probably about three-quarters the size of Pluto. Moreover, Easterbunny is now the third Kuiper belt object, after Pluto and Xena, known to have a surface covered in frozen methane. For decades, Pluto was the only known methane-covered object beyond Neptune, but “now we suddenly have three, in a variety of sizes at a variety of distances, and can finally try to understand Pluto and its cousins,” says Kris Barkume, a PhD student working with Brown.