A fanciful representation of the end of the world. Grab your hard hat! This stone looks a lot larger than the one that wasted the dinosaurs.
Movie still from Armageddon.
© 1998 Touchstone Pictures.
Is this science?
The asteroid debate raises a larger issue. How can scientists reach radically different conclusions from similar data? The optimists say there are just three chances of a catastrophic impact every million years. Yet given the intensity of human population and habitation, smaller objects that might once have been benign may be fatal today, and that in our interconnected world, the ensuing war, famine and chaos could be more destructive than the actual impact.
The optimists deride the historical and anthropological signs that impacts spelled doom for civilizations as exceedingly flimsy. The pessimists say that since many smallish impacts probably occurred over the past 10,000 years, it makes sense to search for their effects, one of which might be the sudden demise of civilizations.
The optimists demand to see the evidence, but the pessimists counter that the most convincing signs -- craters -- are misleadingly rare. Most of the Earth is covered by water, where craters don't form, and only about 3 percent of asteroids are iron. The remainder, like the Tunguska object, are stony objects that break up in the atmosphere. Thus, as asteroid hunter Gehrels says, "3 to 4 percent of asteroids would come through -- that's an accurate number."
Furthermore, as he observes, craters that do form are eventually wiped out by erosion or plate tectonic movement.
The optimists say that for any individual, the chance of asteroidal assassination is equivalent to the chance of dying in a jet crash. The pessimists say that a civilization is, well, a precious thing to waste, so it only makes sense to look for objects large or small before they come looking for us. Both sides agree that a well-aimed Tunguska object could obliterate any city on the planet.
Aristotle 'n asteroids
Perhaps it's not a case of scientific disagreement but rather a philosophical dispute. As Morrison says, "Given the same data, people will still come to different conclusions about the correct resources to devote to the search [for various types of asteroids]. It's a perfectly legitimate social question about what risks you want to deal with."
Gehrels says completing the search for 100-meter objects would "be a reasonable goal," and notes that Spacewatch is attempting a statistical survey of these smaller but still deadly objects. Nevertheless, he sees signs of progress in the ongoing searches. With carefully chosen words, he says, "The asteroid hazard is the most serious thing that humanity faces, because it's the only one that can eliminate society at once. But we are on the way to taking care of it."
Astronomer Steel, however, is less sanguine. Asked via e-mail if current search programs are adequate, he fired back: "I take it you are joking. There is NO SOUTHERN HEMISPHERE SEARCH PROGRAMME [emphasis his].
Ipso facto, current efforts are not sufficient. However, the only real Northern Hemisphere search projects -- wonderful efforts operated from the U.S. -- are only covering (i) a minor portion of the northern sky; (ii) Not covering that sky to an adequate faintness limit: They are using only one-meter telescopes, and the laws of physics, which may not be contravened, dictate that telescopes with apertures larger than two meters are required... The great scientists are doing the best they can with very limited funds, but globally we are doing rather less than 10 percent of what needs to be done lest we go the way of the dinosaurs."
The controversy continues in our asteroid attack bibliography.
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