Pluto fired
Pluto is no longer a planet.
And in the end, it was probably the only solution that made sense. If Pluto and 2003 UB313 were to be considered planets, it would have been impossible, finally, to exclude the hundred or so other sizable, round Kuiper Belt objects with eccentric orbits out there.
As it is, we have eight planets, all of them orbiting on the same plane and all of them something other than big iceballs. It's a sad day, in many ways. But in retrospect, the IAU couldn't have made any other decision.
Also sadly, the article- along with numerous blogs mentioning this story- continue to wrongly assert that "Xena" was ever intended as even a nickname for 2003 UB313 outside the small circle of astronomers who discovered it.
It was a joke, people. They called another object they discovered on Christmas Eve "Santa," and its moon "Rudolph!"
Comments
First, how does that disqualify it? It still orbits the sun, and still is spherical.
Second, if that's the thing that makes it a "dwarf planet," and not its size, why is the term "_dwarf_ planet"?
The eight "classical" planets all orbit on the same plane, known as "the ecliptic" (from our perspective, the path of the Sun throught twelve constellations of the Zodiac).
Pluto, 2003 UB313, and the other Kuiper Belt objects don't.
"Dwarf planet" is mean to distinguish Pluto and other objects filling this definition (as yet unnamed) from the eight classical planets. The distinction was also made in the initial committee recommendation to define ten bodies- including Pluto, Charon, Ceres and 2003 UB313- as planets. The difference is that under the scheme the IAU finally adopted, "dwarf planets" would be a category more or less like "minor planets" (i.e., asteroids)- something less than
full planets.
The IAU requires that a true planet have "cleared its area." By that it means that it has to be the dominant object in its own vicinity. Well, tiny Pluto just isn't. Neptune is.
More than that, Pluto doesn't even dominate the Kuiper Belt. There are dozens of objects similar to it and only slightly smaller- and at least one that's larger.