spacetoday.net: "Tenth planet" only slightly larger than Pluto

Posted: Wed, Apr 12, 2006, 2:07 PM ET (1807 GMT)
Xena illustration from April 2006 (STScI)

New observations of an object that last year was unofficially proclaimed the solar system's tenth planet have revealed that the world is only slightly larger than Pluto. The object, officially known as 2003 UB313 but unofficially nicknamed "Xena", was estimated last year to be about 30 percent larger than Pluto. New observations by the Hubble Space Telescope, released Tuesday, found that 2003 UB313, with a diameter of 2,400 kilometers, is only slightly larger than Pluto, which is approximately 2,300 kilometers in diameter. The decrease in size is because the object's surface is far more reflective than previously expected, reflecting 86 percent of the incident light. That would make 2003 UB313 more reflective than any other planet or moon in the solar system except for Saturn's moon Enceladus, and may be evidence of a tenuous atmosphere that has frozen on its surface. Astronomers have yet to decide whether 2003 UB313 should be formally classified as a planet, and, if so, what its name should be.