Pluto

[gfish]

For some reason the subject of Pluto's status has come up several times recently. (Probably because I've been reading a lot about planetary formation.) I certainly agree that it isn't a planet, but I'll take an even more radical stance: Earth isn't either.

That's right. I don't think Earth should be classified as a planet.

To be more precise, I think it is ridiculous to place Earth (or Mercury or Venus or Mars) in the same class as the gas giants. If you were an intelligence evolved entirely outside the context of planets and you started looking at solar systems, I think you would break things down as follows: stars - planets (gas giants) - random rocky crap (us). Our hypothetical alien intellects (vast and cool and unsympathetic), not obsessed with our particular form of wet and squishy life, would barely even notice the inner solar system. To think that the object we live on must necessarily be grouped with Jupiter and Saturn is pure provincialism. It's nothing more than an updated form of geocentrism.

But at least this means the Kuiper Belt objects would be in the same category as the Earth, so I have to assume those upset about Pluto will be happy.

Comments

[peteralway.livejournal.com]

Actually, I think that it's as sensible to call a planet "a (celestial) body a person could walk on." The Jovian planets can be booted out of the club because they have no surface, and once asteroids get so small that a conventional walking-bace step sends you off at escape velocity, they are too small to count as planets.

In all seriousness, I think that for nearly 80 years, planets were exemplefied by a list of nine, and since the toppling of the geocentric model every known object on that list was counted as a planet, the list itself is a good source of a functional definition of a planet.

As far as I can tell, Pluto was dethroned in large part because new Kuiper Belt objects larger than Pluto "threatened" to create a long list of planets. It was a reductio ad absurdium argument that "pretty soon we'll have 20 or 30 so-called planets," as if progress in astronomy were a bad thing.

Personally, I think Eris is the tenth planet and if astronomers discover more Kuiper-belt objects bigger than Pluto, then bully for them!

I think it's perfectly reasonable to define planets as objects orbiting a star that are too small for fusion in their cores, and are above an arbitrarily defined size; and these include terrestrial planets, jovian planets, kuiper-belt objects, and some categories that extrasolar planet discoveries are starting to suggest.

Defining terrestrial planets out of the club is to completely discard the common understanding of the word, and would be dictation language beyond reason. Personally I think defining Pluto off the list is pretty darned close to the same thing--the IAU doesn't own the English language.

Yeah, I'm a Plutophile.