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Tuesday, June 24, 2008

Remembering Pluto

Sure, Pluto's path around the Sun is rather eccentric, maybe even chaotic. But it has three moons -- Charon, Hydra, and Nix -- and its gravity is strong enough to cause perturbations in the orbit of Uranus (which isn't nearly as horrible as it sounds). And yet it has been demoted from planet to planetoid.

Make that plutoid.

According to the International Astronomical Union, "plutoids are celestial bodies in orbit around the Sun at a semimajor axis 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 neighbourhood around their orbit."

I know exactly what you're thinking: "Ceres is a dwarf planet. Does that mean it's now a plutoid too?" The answer is no. Ceres is located in the asteroid belt between Mars and Jupiter, so it doesn't fit the definition of a plutoid. (Duh!) The IAU has not yet decided what to call Ceres-like dwarf planets.

Alas, Pluto, we hardly knew ye. You may no longer be considered a planet, but that doesn't mean we can't still be friends.

1 comment:

Chris Wilde said...

So if Pluto is bigger than Mercury, does that make Mercury a mercuroid? I think it would be easier just to stick with planet, or not a planet, and declare a moratorium on "-oids". Well, unless they find some new object out there that they can name "Hemorrhus", then we and all the 12-year-olds in the world could have some fun. Yeah, yeah, I know, that would be somewhere near Uranus.

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