Our unofficial 10th planet Xena is unvealing itself in mysterious ways. New Hubble Space Telescope images released this week show that Xena's smaller than originally thought - with a diameter of 2384 km, or about 5% larger than Pluto.

But the weird part is that Xena reflects 86% of sunlight whereas Pluto only reflects 60%. The only known object in our solar system known to have a higher reflectivity is Saturn's moon Enceladus.

Scientists have proposed two scenarios to explain Xena's high reflectivity. In one, a jet of methane leaks continuously from Xena. The methane jet freezes as it emerges, continually blanketing the surface with fresh snow.

What's the heat source that could drive such activity? "Beats me," says planetary scientist Rick Binzel of the Massachusetts Institute of Technology. He notes that gravitational tugs from a neighboring moon sometimes generate heat within a body, but Xena's moon is too small to do that.

Another source of heat, sunlight, would penetrate only a few tens of meters below Xena's surface and would probably have long ago depleted the reserves of methane there.

In the other model, the planet has a methane-rich atmosphere created during the portion of its 560-year-long orbit when it's nearest the sun. As Xena speeds away, the atmosphere freezes on the surface as a bright frost. However, Brown says, it's not clear that such frost would be bright enough to account for the shininess of Xena's surface.

Source: ScienceNews