Kuiper belt object 2003 UB313

The NASA/ESA Hubble Space Telescope resolved Kuiper Belt object Xena, for the first time, and found that it is only just a little larger than Pluto.

Ground-based observations suggested that Xena was about 30 percent greater in diameter than Pluto, but Hubble's Advanced Camera for Surveys images, taken on Dec. 9 and 10, 2005, yielded a diameter of 1,490 miles with an uncertainty of 60 miles (or about 2400 kilometres with an uncertainty of 100 kilometres) for Xena. Pluto's diameter, as measured by Hubble, is 1,422 miles (about 2290 kilometres).