Minor planets, major thoughts

Contributed by
Aug 22, 2008
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I link to Emily's blog at The Planetary Society quite a bit, but that's because a) she's really good, and b) we agree on a lot of things.

For an example of (b), read her post about the definition of "planet". I'm still not swayed by a lot of what I've read of others' opinions, but Emily seems to be on the right track. She says this:

Frankly, I think it's much less important for a student to be able to name all the planets than for the student to understand the basic structure of the solar system: that Earth is one of many worlds that orbit around the Sun at different distances. Each of these other places has similarities to and differences from Earth. Studying these other worlds is both fascinating in its own right and also helps us understand our own planet. And the way we study other worlds is by looking at them from Earth with telescopes and by visiting them with the spacecraft that leave Earth (most of them leaving Earth forever) to wander our solar system, serving as our eyes, ears, hands, and sometimes even noses.

Even after discussions with Alan Stern, I'm still struggling to figure out if this is merely a semantic argument, or a truly scientific one. I may need to buy Alan a drink and talk this over some more. If I do, I'll let you know. I do need to watch the videos of the planet definition debate first, though.

But back to Emily: for an example of (a), she has posted an astonishing series of pictures about all the smaller worlds (asteroids and comets) visited by spacecraft... and then put up an incredible image showing their relative sizes. The difference between the comet Itokawa and even a smallish asteroid is really rather shocking. If you sat Itokawa on the Earth's surface, it would be a fair hill, maybe a little difficult to bike up, but that's about it. Whereas even small asteroids are bigger than Mt. Everest.

And those things sometimes hit us. Brrr.