10th Planet Slightly Larger Than Pluto

"An icy ball discovered last year in the outer solar system is only slightly larger than Pluto, casting doubt on previous estimates that the so-called 10th planet was significantly larger, scientists reported Tuesday.

Previous estimates by ground-based telescopes suggested the object known as 2003 UB313 was 30 percent bigger than Pluto.

But the latest measurement by the Hubble Space Telescope has a smaller margin of error and is probably a more accurate estimate, said lead researcher Michael Brown of the California Institute of Technology.

According to Hubble, UB313's diameter measures 1,490 miles, give or take 60 miles. Pluto is about 1,422 miles across.

Brown previously reported that UB313 could be up to 2,175 miles in diameter based on its brightness. He said he was surprised by Hubble's findings, which will be published in an upcoming issue of Astrophysical Journal.

The discovery of UB313, which Brown nicknamed Xena, reinvigorated the debate about what is considered a planet. Some astronomers have questioned whether Pluto should keep its planetary status, while others say UB313 should be the 10th planet because it is bigger than Pluto.

The International Astronomical Union, which oversees the naming of planets, has not taken a stance on the issue.

If it is determined to be the 10th planet, UB313 would be the farthest-known body in the solar system."