The Sciences

Another asteroid shaves the Earth

Bad AstronomyBy Phil PlaitMar 18, 2009 2:39 AM

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I just saw on Universe Today that asteroid 2009 FH -- a tiny thing, maybe 20 meters across -- will pass the Earth at a distance of about 80,000 km, about 1/5 the distance to the Moon and well above our geosynch satellites. The most recent numbers I've seen show that closest approach will be on March 18 at noon UT, just a few hours from now as I write this. It won't get terribly bright, since it's really small. It's only about the size of a house, which is dinky as these things go. People always ask what an asteroid like this would do if it hit us. Bear in mind this one won't, but if something this size whacked us, it almost certainly wouldn't reach the ground (unless it were an iron asteroid, which are less common than stony ones). Instead, it would burn up in our atmosphere, probably exploding several kilometers up. It might be big enough to generate a shock wave that could cause grief on the ground; recent work showed the Tunguska blast in 1908 was probably from a rock 30 - 60 meters across. So this one would do far less damage, because it would have had less than half the mass of that one at best. So another one slips past us. Let me say this again: while things like this make most people more nervous, it actually makes me happier. It's not that more of them are passing, it's that we're getting better at spotting them! And that means when the day comes when one of these big enough to do serious damage has us set in its crosshairs, we may know about it far enough in advance to do something about it.

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