Saturday, February 28, 2004
Easterbrook's blog discusses Earth's most recent "near miss," which passed earlier this week with little publicity, at least relative to less momentous subjects that get a lot of publicity. Easterbrook's argument is that we should consider reframing NASA's mission as planetary defense, rather than screwing around with costly and scientifically unproductive manned missions to Mars. But is Earth really at risk? Perhaps more than most of us realize:
The gargantuan Chicxulub meteorite, which left a 186-mile-long depression at the tip of the Yucatan Peninsula, probably killed off the dinosaurs. But that was 65 million years ago. Big rocks from space only fell in the primordial past, right?
In 1908, an object 250 feet across hit Tunguska, Siberia, flattening trees for 1,000 square miles and detonating with a force estimated at 10 megatons, or 700 times the power of the Hiroshima blast. Had the Tunguska rock hit Moscow or Tokyo, those cities would have been seared out of existence. In 1490, an estimated 10,000 people were killed when a mid-sized meteorite hit China. In the year 535, a series of mid-sized meteorite strikes around the globe kicked enough dust and debris into the atmosphere to cause several years of cruel winters, helping push Europe into the Dark Ages. Ten thousand years ago, just as modern Homo sapiens were making the first attempts at controlled agriculture, something enormous struck the Argentine Pampas, obliterating a significant chunk of the South American ecology with a force thought to be 18,000 times that of the Hiroshima bomb.
Asteroids and comets are hardly just a danger from the primordial; loads of them drift through the solar system to this day. Estimates by the Space Science Institute of Boulder, Colorado, suggest that perhaps 500,000 asteroids roughly the size of the Tunguska rock wander near Earth's orbit. Much spookier are asteroids big enough to cause a Chicxulub-class strike. Roughly 1,000 such space rocks are believed to exist in Earth's general area, some capable of killing many millions when they strike, then plunging the planet into a years-long freeze while showering the globe with doomsday rain as corrosive as battery acid. Asteroids large enough to cause years of deep-freeze and many species extinctions are estimated to strike Earth at least every few hundred thousand years.
A law school professor of mine (James Krier) used to talk about "zero-infinity" problems, particularly in the context of environmental regulation. Zero-infinity problems were (in Krier's classroom, in any case) risks with an approaching zero chance of occurrence, but with potentially catastrophic consequences. As I recall, his archtypical example was the risk of a non-Russian nuclear power plant melting down. His main point was that it is extremely difficult for either courts or legislatures to contend with zero-infinity problems, mostly because policies to manage these risks inevitably divert resources from more probable risks. If we ban or excessively regulate nuclear power so as to avoid the risk of meltdown, are will increasing the losses we suffer from more extended reliance on fossil fuels?
In any case, the asteroid collision scenario is the mother of all zero-infinity problems. The fact that that Hollywood has made any number of movies around the theme only hurts the political case for Easterbrook's proposal. Any President who proposed that NASA reframe its mission to defend the Earth from collisions would end up squarely in Jay Leno's crosshairs. This is too bad, because anybody who has read Larry Niven's and Jerry Pournelle's classic novel Lucifer's Hammer (which TigerHawk highly recommends) knows that all sorts of horrendous things will happen if we do get hit.
I am actually a big fan of the Mars mission that Easterbrook derides, but largely because I believe that humanity cannot forever keep all its peeps in one basket, so to speak, and survive. We need to spend the next millenium learning how to move off the planet permanently, and to me that requires manned missions. However, my concern springs from my view that Earth is at risk, over the long-term, for planetary catastrophe. If NASA's mission is reoriented to planetary defense, we would at least eliminate one source of catastrophic risk and thereby defer the need to distribute ourselves off the planet. Also, my guess is that the technology developed to defend Earth would greatly facilitate other space adventures in the second half of the twenty-first century, so we'll get to Mars eventually. As Easterbrook says, Mars will always be there.