Thursday, August 17, 2006

Planets out the wazoo!

By now, everyone and their dog has chimed in on the IAU's proposed new definition of what constitutes a planet. And to think that up until yesterday folks were focused on the "Is Pluto or isn't it?" angle. The IAU threw all that into turmoil, basically saying that if a celestial object has enough mass for its gravity to crush it into a spherical shape, then it's a planet. This seems like a good idea at first--a strict scientific measurement that's fairly straightforward and unambiguous. Except that this definition returns the astroid Ceres to the ranks of the planets.

Although I'm a big fan of Ceres, even I think redefining the term "planet" to include objects that small (less than 600 miles in diameter--we're talking Texas folks. Texas is big, but not planet-sized!) is going too far. The gravitational factor is a good indicator of planethood, but the concept of "planet" carries more, uh, gravitas to it than that. This definition opens the door to hundreds, if not thousands of icy Kupier Belt objects being named planets. Can open, worms everywhere. This "cure" is worse than dismissing Pluto as a planet all together.

So if I were king, how would I handle this? I'd set an arbitrary limit of 2,000 km for a true planet's diameter in addition to the other parameters listed in the new IAU definition. Why? Because that's a nice round number which just lets Pluto in the club but doesn't allow much wiggle room for anything smaller. Other than that, it's completely and utterly arbitrary. Deal with it. So, sorry Charon. Shared barycenter or not, you're too small to be a double-planet with Pluto.

Those objects that fall below my 2,000 km threshhold, yet meet all other IAU criteria, well, there's a ready-made term for them. Call them "Planetoids"--an intermediate body between the full-scale planets and irregular asteroids. I mean, "planetoid" has pretty much completely fallen into disuse, and is little more than a poor-man's synonym for asteroid these days. This would bring a little luster back to the venerable term, and also offer Ceres something of a consolation prize in the process. Am I a genius or what?

Now Playing: Tom Petty & the Heartbreakers Live at the Fillmore

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