Xena, unofficially called the 10th planet, is the second-most-shiny known object in the solar system, new observations show. Scientists are scrambling to explain where Xena got its sparkle. Some suggest that it might have enough heat to belch methane, despite being in the coldest region of the solar system.
The new notion of Xena arises from Hubble Space Telescope images that were released this week. The images reveal that Xena, the most distant known object in our solar system, isn't quite the big shot that scientists had thought it was.
Researchers have difficulty determining the size of remote denizens of the solar system because a large object that reflects a small amount of sunlight looks the same as a small object reflecting a lot of light.
But for Xena, the sharp Hubble pictures erase that ambiguity.
The relatively small size shown in those images indicates that the body reflects 86 percent of sunlight. Brown says he was "thoroughly shocked" by that finding. Researchers had assumed that Xena's surface was similar to that of Pluto, which reflects 60 percent of sunlight. Saturn's moon Enceladus, recently shown to be shooting out a geyser of water vapor is the only solar system object known to have a higher reflectivity, notes Brown.
The distant sun shines on Xena, often called the 10th planet, in this illustration. Inset: The Hubble Space Telescope image that revealed Xena's size for the first time.
A. Schaller, NASA, ESA; (Inset) Brown, NASA, ESA