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

[orawnzva.livejournal.com]

We already have a term — "gas giant" — for the category of objects you propose. There are a limited number of reasons to prefer one usage of a term over another. One is closeness to an original meaning; the original meaning of "planet" is intrinsically geocentric as neuro42 points out.

Another is current common usage; this could mean either common usage within the astronomical community, including the idea that a planet is overwhelmingly the largest object in its orbit, since the asteroids are already excluded, or the vernacular meaning whose exact semantics is vague, mainly rooted in the explicit list of planets we learned in school and with the proviso that other objects "like those" would count as planets if discovered.

A third reason to prefer a usage is usefulness, and this must always mean usefulness to some users of the term. Yes, Earth is puny when set beside the mighty Jupiter. Should we then defer to the inhabitants of Jupiter in all questions of terminology— oh, right, as far as we know Jupiter is uninhabited. The question then becomes, which meaning of this term is most useful to us in our current situation (where our situation is taken to include the existence of documents which employ the term in the senses in which it has historically been used up to now)?

[caladri.livejournal.com]

The thing is, we're clearly letting scientific dichotomies dictate what we call a planet these days (if we weren't willing to let science dictate, we wouldn't care whether the IAU said Pluto was a planet) so we should be wary of using dichotomies that are constructed to preserve historical biases, that which would put Jupiter and Earth in the same category and at the same level of hierarchy but define Pluto as less significant than Earth.