A reader writes:

I'm a professional astronomer, and I actually study near-Earth asteroids (NEAs) for a living.  I'm only too happy to question NASA's priorities and whether more funding should go to investigating the impact hazard, but in the interest of fairness and clarity, I'd like to make a few (hopefully short) points with respect to Easterbrook's video.

1) There have indeed been an explosion of NEAs discoveries in the past decade or two.  But this has largely been by design; Congress charged NASA with finding at least 90% of all asteroids with diameters of 1 km or larger by the end of 2008, and with that new focus the rate of discoveries has gone up.  In addition to finding the 1 km asteroids, smaller ones (in some cases small enough to fit in your living room) have also been found.  But in my opinion, this is the best way to leverage our resources: a small increment of money will allow a thorough enough search of the neighborhood that we'll be able to characterize what's out there and determine where we need to focus next.

2) Another part of the problem is that there is no real consensus for what the threshold of risk is at which we would act.   If we decide an asteroid with a 1% chance of an impact is too dangerous to leave alone, then 99 times out of 100 we will have acted in vain.  And unfortunately, our data is rarely precise enough (simply because of the distances and sizes of the objects) that by the time we have even determined if there is a 50% likelihood of impact, it may be way too late.

3) Finally, the legal ramifications are really murky. The United States could undertake an asteroid deflection, and there are at least a few other countries that could also do it if they put their mind to it. But it would require a level of spacecraft reliability that we just don't have.  What happens if in an attempt to avert an impact into Europe, NASA accidentally nudges it into Bangladesh?  What if a smaller impactor would hit the Indian ocean and destroy some smaller island nations, but there was ample time to evacuate everybody? What if nuclear weapons were required for deflection (as indeed they might, since the gravity tractor idea is ill-suited for some cases)?  Now, what if instead of us deciding those questions for instruction to NASA, the Russians or Chinese decided to take the lead?

I think it's good that this debate is happening.  But I think I can assure you that in terms of immediate threats to your health, you should focus instead on making sure you exercise and eat lots of fiber.

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