Comment on Politicians stymie human colonization of space to save make-work jobs

Sun, 18 Jul 2010 17:12:45 GMT

Is it that insignificant?

Asteroids larger than 1 km hit the Earth about every 500,000 years. (source). That's in the large-scale devastation but not extinction range. Indeed, even asteroids a few 10s or 100s of meters can cause major devastation. The object that caused the Tunguska event is estimated to be between 50-80 meters , and such impacts occur every few hundred years or. Historically such events have had minimal loss of human life, but that's partially due to much less of Earth being populated by humans than it is now. So even without worrying about existential level threats, asteroid impacts pose a substantial risk to human life. As the population grows that risk will become more severe.

How frequent are extinction level asteroid collisions? There's some disagreement there but the ratio seems to be between about 1 per 40-200 million years. That seems plausibly like a low risk existential threat, but how does one compare other existential risks? How does that compare to the chance of say global thermonuclear war or the probability of a uFAI arising? If one presents a very low probability on a uFAI, or put a low probability not on a uFAI but on an AI going FOOM, then this becomes potentially more relevant.

Note also that one doesn't really need an existential level asteroid impact to permanently ruin human life. If we use up enough resources on Earth, especially fossil fuels, then it may not be possible to bootstrap ourselves back up to modern tech levels if the tech level is substantially reduced. As we use more limited resources this risk becomes more serious. We're not anywhere near using up the deuterium supply, but that's also limited as is the supply of U-235 which is much closer to depletion (although again, not very close). This permanent resource crunch after a major civilization setback is enough of a risk that Nick Bostrom takes it seriously (see first link given above.) An asteroid in the 3-5 km range if it hit in a bad way could cause this sort of scenario.

The main problem with the asteroid type event is that there's very little we can do about it. Breaking up an asteroid into little parts won't actually do much if they still impact Earth since the total kinetic velocity delivered is still about the same. There's more of a chance at potentially redirecting an asteroid if one attaches a solar sail or a large nuke at just the right spot. But all such options require knowing about the threat a while in advance.

There are two other point that supports a space program as a existential risk reducer which Timtyler didn't touch on but are worth bringing up: 1) Even if we can't construct self-sustaining colonies yet, every bit we go in that direction increases the chance that we will be able to have such colonies before any event occurs that wipes out or substantially reduces human life on Earth. 2) There are many space based extinction threats other than rogue asteroids where having advance warning even by a few days or hours could substantially reduce the risk. These include supernova risks primarily from IK Pegasi A and Betelgeuse. Our current estimates put both of these as low probability events. Under current estimates Betelgeuse is too far away given the predicted supernova size. But there's a not insignificant chance that our models are wrong and even a small bit off could substantially ruin our day. IK Pegasi A is close enough that if it went through a a Type Ia supernova now (well a 150 years ago), it would easily be an extinction level event. It is likely that the star will go through such at some point in the future, but current estimates put that a few million years in the future. But again, modeling issues could make this drastically wrong (although the chance of a modeling error is much smaller than with Betelgeuse.) Then there are other more exotic and as yet difficult to estimate threats such as gamma ray bursts and rogue brown dwarfs.

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