Bad Astronomy
The entire universe in blog form
Aug. 1 2006 11:54 PM


Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


It's an impressive animation of what would happen if an asteroid -- maybe 100 500 miles across or so -- impacts the Earth. The visuals are stunning, and someone set it to excellent music for the action. I saw it on a TV program not too long ago, maybe a month, maybe on the National Geographic Channel. Does anyone know the source? And for that matter, what music it is? I want to find it!

Anyway, its depiction of a massive impact is unflinching and brutal. I'll stress right here that the odds of anything this size hitting us even in the next million years are slim to none. We know of every asteroid this size in the solar system out to terrific distances, and none is slated to ruin our day (or millennium).

But an impact like this would wipe out everything. Everything. As far as I can tell, the depiction there is pretty accurate. Notice how the impact appears to be in slow motion-- in reality, the speed is something like 10-20 miles per second. It's just that the rock is so big, a hundred miles across, things appear to move slowly. The expanding ring of death is moving at the speed of sound, 700 miles an hour. You can see continents lifting up as the shock wave moves through them, vaporizing water, rock, metal. The oceans boil, the crust melts, and, well. There you go.

The only real error I saw, I think, is when the shock wave encircling the Earth finally closes up when it reaches the opposite side of the planet from the impact point. The shock would eject a plume from the other side, like squeezing a watermelon seed between two fingers. We see evidence of this on other bodies; ringed features opposite giant impact craters, where the shock wave from the impact converged on the other side of the world.

Cripes. My nightmares are things like this. I'm glad there are folks looking for these bullets, and plans to do something about it. Maybe some day we'll take this threat seriously enough to really fund it.

Tip o' the Whipple Shield to the folks over on the Bad Astronomy/Universe Today bulletin board who were discussing this. And oh-- maybe there is a way to stop these things that NASA never thought of...