Posted: Sun, Oct 2, 2005, 2:24 PM ET (1824 GMT)
Astronomers who earlier this year reported the discovery of a distant solar system object larger than Pluto now say that a sizable moon orbits it. Caltech astronomers said Keck telescope observations last month of 2003 UB313, informally nicknamed "Xena", revealed the existence of a moon. Astronomers estimate that the moon, nicknamed "Gabrielle" after the fictional Xena's sidekick, is about one-eighth to one-tenth the size of Xena, making it about 250 kilometers in diameter. Additional observations of the planet and its moon are planned for later this year using the Hubble Space Telescope to pin down the object's size, orbit, and mass. The discovery was made by the same group that announced in late July that it had discovered Xena, estimated to be somewhat larger than Pluto. That has led many to conclude that Xena is the solar system's tenth planet, although the International Astronomical Union has yet to make an official decision on the object's status.

Related Links:

•  AP article
•  Honolulu Star-Bulletin
•  Caltech discovery information