Wednesday, October 25, 2006

Don’t Mourn for Pluto

Don’t Mourn for Pluto
by Dave Adalian

After 76 years as the Solar System’s ninth planet, Pluto suddenly finds himself all alone out in the cold.

Of course, he’s probably used to that by now.

At a meeting of the International Astronomical Union last month, Pluto was stripped of its status and reclassified as a “dwarf.”

The poor little guy. But, does he deserve it?

Truth be told, Pluto is a whole lot different than his Sun-hugging cousins.

First off, he’s tiny, about half the diameter of Mercury, smallest of the rocky inner planets, smaller than many of the other planets’ moons, including Earth’s. His size really isn’t all that odd, except Pluto lives in the land of the gas giants, the smallest of which, Neptune, could hold 60 Earths if it were hollow.

Making Pluto even odder, his axis is inclined so much his north pole points at the Sun. But, he’s not alone here. Uranus, too is tilted on its side.

Also, the largest of Pluto’s three moons, Charon, is almost half as big as he is, making them a double system in the minds of some astronomers. And again, he’s not alone in this. Earth and the Moon are somewhat similar in size and considered a double planet in some circles.

So, what’s the fuss?

Well, the IAU’s new definition of a planet says planets have orbit the Sun, have to be round, can’t orbit another planet and have to clear their orbit of other objects. It’s that last item that’s gotten Pluto in hot water.

Pluto takes a unique path around the Sun. Not only is his orbit tilted, taking it up and down like a horse on a merry-go-round, that orbit is also highly eccentric, sometimes taking the small body inside the orbit of Neptune.

Pluto doesn’t move like the other planets do because it is one of the largest objects in the Kuiper Belt, and since there are thousands of other Kuiper Belt objects sharing Pluto’s orbit, he just doesn’t fit the IAU’s new definition. So, out he goes.

In general, astronomers aren’t an excitable bunch, but the decision last month has professional stargazers around the world crying foul. The vote, held on the last day of the IAU’s meeting, only included the opinion of a handful of the body’s 10,000 or so members, many of whom are calling for another vote on the matter.

So, Pluto might regain his status as a planet the next time the IAU comes together. Either way, Pluto probably doesn’t much care what people on a planet so far away it can’t even be seen from where he sits call him.


This column originally appeared in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register on Sept. 14, 2006.

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