Pluto is a Plutoid

Okay, look, sometimes a governing agency has to make a tough call in order to promote future stability and, for the long term, make things simpler, smarter and helpful for all concerned.

This is not one of those times.

The International Astronomical Union, belligerently continuing its anti-Plutite policies, has given a new designation to poor little Pluto. Pluto’s not a planet anymore. It’s a Plutoid.

Okay, all joking aside, I realize that there are good reasons to say Pluto isn’t a planet. For one thing, there are about 70,000 things like it in the Kupier Belt. And, according to the IAU, Pluto is missing one huge characteristic of a planet: it does not “dominate its neighborhood” (scroll down to the bottom of that short article for the relevant part). In short, a planet should pwn all the asteroids, comets, and whatever else gets in the way of its orbit. Pluto, even though it has its own moon (Charon), itself has a weird orbit and occasionally gets pwned by Neptune. Thus, not a planet, but a “dwarf planet” — a round celestial object that doesn’t dominate its neighborhood but isn’t something else’s satellite. Or, as per the new ruling today, a “plutoid.”

But here’s where the IAU got stupid. They defined plutoids as:

… celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit.

Now why did they have to add that bit about “a distance greater than that of Neptune”? See, if they hadn’t, then Ceres could be called a plutoid too, and things would be nice and tidy. Instead, now we have dwarf planets, some of which are plutoids, some of which aren’t. I suppose if you want to focus only on the dwarf planets in the Kupier Belt or beyond, the term might be slightly meaningful. But really, couldn’t just give an inclusive definition for all similar objects? Now generations will have to fight about Ceres as well?

It’s very interesting to me how political and volatile the field of astronomy, what with its Relativity and its String Theory and its M-Theory and now its planet-naming, has become so controversial. I think all these controversies highlight just how important astronomy has become to humanity’s vision of itself. 

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[...] Original post by Carlos [...]

June 18th, 2008

Celestial Objects » Pluto is a Plutoid