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Distant Iceballs

December 7, 2010

We all know that Pluto isn't a planet anymore. Grieve not for the little world, though, because it's picked up a whole lot of other designations to make up for the one it lost.

At the top of the listings, it's a dwarf planet. That means it's massive enough to pull itself into the shape of a ball, but not massive enough to sweep other objects out of its path. Pluto's the first dwarf planet, but it's not alone -- and it's not even the biggest. That distinction is held by an object known as Eris; more about that tomorrow.

Pluto is also a plutoid -- a dwarf planet that orbits beyond Neptune, the eighth planet out from the Sun. That category includes all the known dwarf planets except Ceres, which is the largest member of the asteroid belt.

And Pluto also tops the list of plutinos -- objects that complete two orbits of the Sun for every three orbits that Neptune makes. There are several of those, including one that's like a mirror image of Pluto -- it's farthest from the Sun when Pluto is closest and vice versa.

That object is known as Orcus, and like Pluto and the other plutoids and plutinos, it's also known as a Kuiper Belt Object. The Kuiper Belt is a broad ring that encircles the Sun beyond the orbit of Neptune. It probably has millions of icy inhabitants. Some are tiny, while objects like Eris, Orcus, and Pluto are fairly large -- worlds that are dwarfs among planets, but giants in the frozen realm of the outer solar system.


Script by Damond Benningfield, Copyright 2010


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