Thursday, June 08, 2006

Empty Space

Space is really big. And really, really empty.

If you look at a detailed map of our solar system, you’d think that it’s pretty crowded between the orbits of Mars and Jupiter. There are thousands — millions — of little planetoids and asteroids floating around out there. Some of them have wonderful, exotic names like “Massalia”, “Alexandra”, “Petrina”, and “Seppina”. Others have sterile, provisional names like “(29075) 1950 da”, “(3360) 1981 va”, and “(15760) 1992 qb1”. It seems as though the sky should be filled with them.

As we started sending spaceships to Jupiter and beyond, many people expressed dismay that our daring little robots would be pelted to smithereens by flying space rock. As a child, I remember seeing movies where spaceships would fly through asteroid belts and it was like pushing your way through the crowd in the mall on the day after Christmas to buy wrapping paper at half price.

But after 30-some years of trans-Jovian exploration, not one craft has been as much as brushed by a pebble. Have we really been that lucky?

No, space is really that empty!

Cosmic scales are really hard to imagine. Let’s put it in perspective.

If the sun were the size of a basketball, the earth would be smaller than the round head of a push-pin. And it would be about 100 feet away.

And what would be between the two? Nothing. Well, Venus and Mercury would be floating around — even smaller than the earth. But they’d be just as likely as not to be floating around on the other side of the sun — far, far away. The largest of the asteroids would be smaller than dust particles in smoke.

Space is so empty that the odds of a spaceship being struck by a stray asteroid are literally billions to one against. You have to try really hard to catch up with an asteroid. We’ve sent a couple of craft specifically to track some asteroids. And we’ve gotten some good pictures of them as a result. But it ain’t easy, even when you’re trying.

So the guys at nasa had a special challenge recently with their New Horizons spacecraft. It was launched last January and is currently speeding toward Pluto faster than any craft has ever traveled before. So fast, in fact, that it’s already going through the asteroid belt.

The New Horizons project team wanted to have a chance to test some of their navigation and imaging equipment. After all, there’s not much else to do while you’re coasting along on the way to the most distant planet in the solar system. So they decided, hey, if we’re going through the asteroid belt, let’s see if we can spot one.

Yep. They weren’t concerned about being hit  by one. They were trying to even find  one.

Quite by coincidence, they found a tiny asteroid that they were flew close enough to track. They found and photographed asteroid 2002 jf56. It’s a little rock, about one-and-a-half miles across. At the time, it was more than 63,000 miles away. The most powerful of New Horizon’s digital cameras resolved the asteroid only to a couple of pixels.

So a casual cruise through the most densely populated neighborhood of our solar system yielded a chance encounter with a tiny rock tens of thousands of miles away. The paradox of space is that it is both crowded and empty at the same time.

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