The 10th Planet

Pluto, the 9th planet was discovered in 1930. Since then, astronomers have searched for a 10th planet beyond the orbit of Pluto. Until recently, all that's resulted from this are number of unconfirmed reports.

The 10th planet has now (2006) been officially named Eris and nicknamed "Xena" by its discoverers on april 19,2006. It has an estimated diameter at 2700 km, larger than Pluto's 2320 km diameter. It's three times farther from the sun than Pluto is. New images from the Hubble Space Telescope show that the unofficial 10th planet measures 2,384 kilometers (1,490 miles) across. This makes it a little larger than Pluto, which is 1,422 miles wide. And it's surprisingly shiny. It also has a moon, Dysnomia and nicknamed "Gabrielle", discovered in 2005.

Gabrielle

Xena reflects more light than any object in the solar system other than Saturn's moon Enceladus. It reflects 86 percent of the sunlight that hits it. Pluto reflects only 60 percent of the sunlight that hits it. Scientists have two theories why Xena reflects so much light. One idea is that the planet spews out methane gas, which freezes and keeps the surface covered with a blanket of fresh snow. For this theory to be true, something would have to be heating up the planet. So far, there's no obvious source of heat. The other idea is that Xena's atmosphere is full of methane. This atmosphere forms when the planet is closest to the sun during its 560-year-long orbit. As the planet gets farther away from the sun, the methane freezes. But scientists aren't sure whether the resulting frost would be bright enough to fully account for Xena's special sparkle.