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This afternoon I attended a colloquium on Defending the Earth from Asteroid Impacts. The auditorium was packed—apparently a lot of people are interested in avoiding the destruction of life on Earth. :) Our government doesn't seem interested enough, though.

Apparently there's some consensus that one's statistical risk of death from a terrestrial impact is 1 in 20,000. I was surprised at that number; it's about the same as one's risk of death from an airplane crash. I can see how it makes sense given the massive consequences of a large-object impact, despite the low probabiliy. (The risk sounds much less when expressed in terms of the frequency of such impacts.)

The presenter, a member of our department, explained what we know about past terrestrial impacts (Tunguska, K/T), what we know about the composition of asteroids and comets, current efforts to catalog near-Earth objects, and how we might nudge them to a safer speed. (You hear the word 'deflect' often in this context, but it would apparently be more efficient to change the magnitude of the velocity than to change the direction.)

The distinction between asteroids and comets is important. Asteroids come mainly from the belt between Mars and Jupiter. Assuming that sky surveys continue to make good progress, we can expect decades of warning before an asteroid impact. It would probably be possible to defend against an asteroid impact using current technology. A comet impact is less likely, which is a good thing, because they move much faster than asteroids, and their eccentric orbits mean they come from out of the blue, as it were, giving us at most a few years' warning. What we would do with that warning is unclear; we do not have the technology (yet) to save ourselves from a comet impact.

For more information, see NASA's Asteroid and Comet Impact Hazards web site.

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( 2 comments — Leave a comment )
skurtchasor
Apr. 10th, 2005 12:20 am (UTC)
What does "1 in 20,000" mean in this context? As in for every 20,000 asteroids that actually hit, I'm only likely to get killed by one of them?
radhardened
Apr. 10th, 2005 01:30 am (UTC)
I think it means that ∀ person ∈ {humans on Earth, ever}, p(person's cause of death ≡ “bolide impact”) = 0.00005. (Any more mathematical symbols I can misappropriate for you today?)

I would expect that significantly fewer than one in 20,000 bolides (that's my new word for the day!) will kill you. :)
( 2 comments — Leave a comment )