Bigger than Pluto: Tenth planet or icy leftover?

Step aside, Pluto, there’s a new kid in town. Astronomers last week announced that they have detected a body larger and more distant than Pluto. It’s the biggest body found in the solar system since Neptune and its moon Triton were discovered in 1846. But whether the body, dubbed 2003 UB313, qualifies as our sun’s tenth known planet is a matter of intense debate.