spacetoday.net: "Tenth planet" bigger than Pluto

Posted: Thu, Feb 2, 2006, 6:46 AM ET (1146 GMT)
2003 UB313 illustration (NASA/JPL)

Astronomers have confirmed that an object in the outer fringes of the solar system discovered last year is indeed larger than Pluto, raising new questions about whether the object should be considered the solar system's tenth planet. German astronomers used a radio telescope in Spain to measure the thermal emissions coming from 2003 UB313; combined with optical observations of the object, astronomers concluded that the object is about 3,000 kilometers ion diameter, bigger than Pluto, 2,300 km across. 2003 UB313, informally nicknamed "Xena" by Caltech astronomers last year when they discovered it, appeared to be a large body, potentially larger than Pluto, but previous observations could only provide a lower limit on its size. The new size estimate has reinvigorated a debate on the definition of a planet, and whether 2003 UB313 and/or Pluto should be classified as such.