Bigger than Pluto: Tenth planet or icy leftover?
By Ron Cowen
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.
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Many astronomers, including codiscoverer Mike Brown of the California Institute of Technology in Pasadena, says that it’s a no-brainer—if Pluto is the ninth planet, then this object must be the tenth. But others argue that both Pluto and the newfound body, which are tiny compared with the other eight planets, are merely large members of the Kuiper belt, a reservoir containing thousands of icy leftovers from the solar system’s formation.