Tuesday, April 11, 2006

The Planet Police

Robert Roy Britt at Space.com's LiveScience blog has declared that Xena is not a planet and, judging from his somewhat petulant tone, he might just hold his breath until astronomers concede the point:

The world is not “Xena.” Officially, it is 2003 UB313.

But discoverer Mike Brown of Caltech is on a mission to have 2003 UB313 declared a planet, so he gave it a catchy nickname.

Other astronomers, and the good folks at Hubble, should not use the nickname. What they should do is finally agree on a definition for the word “planet.” And 2003 UB313 should not be included.

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[T]hose who write press releases and journalists who cover all this should stop using the nickname “Xena” to describe 2003 UB313. Only when a proper definition for “planet” has been agreed on by the International Astronomical Union can astronomers decide on a name for the tiny, way-out world.
Now, I'll concede that there is no agreed-upon definition of a planet, but so what? If it walks like a duck . . . Indeed, just today, we learn that some astronomers believe Xena may behave very much like a "real" terrestial planet in that it might be geologically active, after a fashion. At least that's a leading explanation for Xena's wildly high albedo (its reflectivity).

Back in February, measurements of the amount light (of certain wavelengths) reflected by Xena's surface suggested that it was about 20-30% larger than Pluto. Recently, though, Hubble successfuly resolved Xena and it turns out that, while bigger than Pluto, it's not much bigger at all -- only about 5% (Pluto's diameter is 2290km while Xena's now appears to be about 2400km). Why then is it brighter than any other object in the Solar System excluding Enceladus (and, of course, the Sun itself). The geological theory holds that methane is extruded from Xena's interior and immediately freezes on the surface to give the planet an albedo akin to that of new-fallen snow. That, though, is as far as the theory goes. No one yet has a theory for why or how Xena extrudes methane.

As far as I can tell, Britt's distaste for "Xena" is a bit childish -- he just doesn't like the name, which has begun to stick, and is appealing to the what's-a-planet-really? debate as a means to wipe the slate clean for a do-over down the road. Whatever the result of the larger what's-a-planet-really? debate, I know this for certain: this far away rock will not be popularly known as 2003 UB313 . . .