So what, exactly, is a planet? Astronomers have been deadlocked over this for years, but a decision may finally be forthcoming, because a thing they discovered last year in the solar system's outer reaches has turned out to be bigger than Pluto.
So if Pluto hangs on to its status -- by no means a slam-dunk -- then the fetchingly named 2003 UB313, which is about 30 percent fatter, probably would have to be a planet, too. The 10th. But if Pluto gets demoted, the solar system will have just eight. Either way, textbooks that refer to nine planets are doomed to obsolescence.
"It's only fair," said astronomer Frank Bertoldi of Germany's University of Bonn. "It's my view that Pluto for historical reasons should remain a planet -- otherwise school kids will be confused. Any object that's bigger than Pluto should also be a planet."
This "new" planet may be bigger than Pluto.