Monday, September 11, 2006

C'mon, Boy!

There's no reason to read the title of this post with a Mickey Mouse falsetto, despite the fact that it is about Pluto. The planet. Or, these days, the dwarf planet Pluto.

Pluto has been reclassified as a dwarf planet by the International Astronomical Union for a variety of reasons. Scientifically, I don't think that it matters very much, but my prediction is that people will react quite negatively to the change, and looking at the status of the Wikipedia article, I think it's going to get ugly, stupid and petty. It feels like it is being demoted, in a way. And most everyone who has gotten past first grade has learned the canonical 9 planets with Pluto at the end, despite the fact that Pluto's orbit is sometimes inside that of Uranus. Nevertheless, the IAU realized that the discovery of objects in the Kuiper Belt and outside the plane of the ecliptic where all the other planets circle (well, ellipse, really) around the sun would lead to a muddle of planetoid objects unless the definition were tightened. And Pluto, while not making the cut as a planet for a handful of reasons, is now a dwarf planet.

This new category now includes Ceres. Ceres is the largest of the asteroids, though it is not made of the same stuff as the other asteroids and is probably independent of them in origin.Ceres looks a lot like a planet, seems to have some sort of atmosphere, and has weird surface features that are at least evocative of a planet. These aren't well understood. Still, being round makes it look enough like a planet that I'm glad that it falls into a category different from all of the other, potato-esque asteroids. It was even listed as a planet in the 1800s, along with a couple of other asteroids, Vesta and Pallas. Until the Pluto dust-up, I didn't know this. Vesta is the brightest asteroid, and usually the only asteroid visible from Earth except under unusually good conditions, though it is much less massive than Ceres, and very tater-shaped. So it doesn't make even the dwarf planet list.

Another dwarf planet that is particularly interesting is Xena, or as it is currently known, 2003 UB313. It orbits way outside the plane of the ecliptic, and is currently about as far away from the sun as it gets. Even so, it is visible with a modest amateur telescope. Xena is not the official name of the planet, but has caught the popular imagination. So much so that its moon is unofficially known as Gabrielle. Xena was one of the reasons for the crisis that lead to Pluto's reclassification, since it is actually larger than Pluto, and is the largest known dwarf planet. I won't place any bets as to whether the IAU will have the imagination to adopt these names, but my guess is they will stick in common usage, just like most of us will always think of Pluto as a planet, despite the astronomy nerds contention that it is a dwarf planet, dammit. Prosperpina (ugh!) and Persephone (not much better) has been suggested, and follows the IAU rules/traditions, but I'll always call it Xena if they pick something as constipated-sounding as that. Who made the IAU planet poohbahs anyway? I certainly didn't vote for them.

UPDATE: The IAU has chosen the name Eris for 2003 UB313. Eris is the name of the goddess of discord, and considering the discord Eris' discovery caused, the name fits. Oh, and Gabrielle? Eris' moon will be known as Dysnomia, the demon of (wait for it) Lawless-ness.


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