With a Bang and Lots of Whimpering

This is the kind of thing that one should not read just before going to sleep at night — as I did last night. The scenario that is discussed should not be new to anybody, but the writer makes it sound so awfully unpleasant and rather unavoidable.

It’s all from the book, A Short History of Nearly Everything by Bill Bryson (2003):

… Sometime in the very ancient past, when Manson [Iowa] stood on the edge of a shallow sea, a rock about a mile and a half across, weighing ten billion tones and traveling at perhaps two hundred times the speed of sound ripped through the atmosphere and punched into the Earth with a violence and suddenness that we can scarcely imagine. Where Manson now stands became in an instant a hole three miles deep and more than twenty miles across. … The Manson impact was the biggest thing that has ever occurred on the mainland United States. Of any type. Ever. The crater it left behind was so colossal that if you stood on one edge you would only just be able to see the other side on a good day. It would make the Grand Canyon look quaint and trifling. Unfortunately for lovers of spectacle 2.5 million years of passing ice sheets filled the Manson crater right to the top with rich glacial till, then graded it smooth, so that today the landscape at Manson, and for miles around, is as flat as a tabletop. Which is of course why no one has ever heard of the Manson crater.

[ … ]

Altogether it is thought — though it is really only a guess, based on extrapolating from cratering rates on the Moon — that some two thousand asteroids big enough to imperil civilized existence regularly cross our orbit. But even a small asteroid — the size of a house, say — could destroy a city. The number of these relative tiddlers in Earth-crossing orbits is almost certainly in the hundreds of thousands and possibly in the millions, and they are nearly impossible to track.

… An object a hundred yards across couldn’t be picked up by any Earth-based telescope until it was within just a few days of us, and that is only if a telescope happened to be trained on it, which is unlikely because even now the number of people searching for such objects is modest.

… I asked them [Ray Anderson and Brian Witzke, geologists at the University of Iowa] how much warning we would receive if a similar hunk of rock was coming twoard us today.

“Oh, probably none,” said Anderson breezily. “It wouldn’t be visible to the naked eye until it warmed up, and that wouldn’t happen until it hit the atmosphere, which would be about one second before it hit the Earth. You’re talking about something moving many tens of times faster than the fastest bullet. Unless it had been seen by someone with a telescope, and that’s by no means a certainty, it would take us completely by surprise.”

… An asteroid or comet traveling at cosmic velocities would enter the Earth’s atmosphere at such a speed that the air beneath it couldn’t get out of the way and would be compressed as if in a bicycle pump. As anyone who has used such a pump knows, compressed air grows swiftly hot, and the temperature below it would rise to some 60,000 Kelvin, or ten times the surface temperature of the Sun. In this instant of its arrival in our atmosphere, everything in the meteor’s path — people, houses, factories, cars — would crinkle and vanish like cellophane in a flame.

One second after entering the atmosphere, the meteorite would slam into the Earth’s surface, where the people of Manson had a moment before been going about their business. The meteorite itself would vaporize instantly, but the blast would blow out a thousand cubic kilometers of rock, earth, and superheated gases. Every living thing within 150 miles that hadn’t been killed by the heat of entry would now be killed by the blast. Radiating outward at almost the speed of light would be the initial shock wave, sweeping everything before it.

For those outside the zone of immediate devastation, the first inkling of catastrophe would be a flash of blinding light — the brightest ever seen by human eyes — followed an instant to a minute or two later by an apocalyptic sight of unimaginable grandeur: a roiling wall of darkness reaching high into the heavens, filling an entire field of view and traveling at thousands of miles an hour. Its approach would be eerily silent since it would be moving far beyond the speed of sound. Anyone in a tall building in Omaha or Des Moines, say, who chanced to look in the right direction would see a bewildering veil of turmoil followed by instantaneous oblivion.

Bryson goes on to speculate about the distance of the immediate blast wave and the probable earthquakes, volcanoes and tsunamis that would follow. Plus the usual cloud of blackness overhead, pelting the world with burning debris. He then continues:

… But let’s assume we did see the object coming. What would we do? Everyone assumes we would send up a nuclear warhead and blast it to smithereens. The idea has some problems, however, First, as John S. Lewis notes, our missiles are not designed for space work. They haven’t the oomph to escape Earth’s gravity and, even if they did, there are no mechanisms to guide them across tens of millions of miles of space.

… Even if we did manage somehow to get a warhead to the asteroid and blasted it to pieces, the chances are that we would simply turn it into a string of rocks that would slam into us one after the other in the manner of Comet Shoemaker-Levy on Jupiter — but with the difference that now the rocks would be intensely radioactive. Tom Hehrels, an asteroid hunter at the University of Arizona, thinks that even a year’s warning would probably be insufficient to take appropriate action. The greater likelihood, however, is that we wouldn’t see any object — even a comet — until it was about six months away, which would be much too late. Shoemaker-Levy 9 had been orbiting Jupiter in a fairly conspicuous manner since 1929 but it took over half a century before anyone noticed.

Interestingly, because these things are so difficult to compute and must incorporate such a significant margin of error, even if we knew an object was heading our way we wouldn’t know until nearly the end — the last couple of weeks anyway — whether collision was certain. For most of the time of the object’s approach we would exist in a kind of cone of uncertainty. It would certainly be the most interesting few months in the history of the world. And imagine the party if it passed safely.

“So how often does something like the Manson impact happen?” I asked Anderson and Witzke before leaving.

“Oh, about once every million years on average,” said Witzke.

“And remember,” added Anderson, “this was a relatively minor event. Do you know how many extinctions were associated with the Manson impact?”

“No idea,” I replied.

“None,” he said, with a strange air of satisfaction. “Not one.”

Of course, Witzke and Anderson added hastily and more or less in unison, there would have been terrible devastation across much of the Earth, as just described, and complete annihilation for hundreds of miles around ground zero. But life is hardy, and when the smoke cleared there were enough lucky survivors from every species that none permanently perished.

I’m not convinced that humans would survive in anything like their current manifestation. I think most of us would die of pure astonishment. I know I would.

In Discovery magazines list of twenty quick-end-of-humanity scenarios, asteroid impact is #1.

See NASA’s list of current known nearish objects, as well as a description of their Near Earth Observation Program. Neither is very reassuring.

[Though not the subject of this post, I want to acknowledge with sorrow that this kind of violent annihilation is not unlike what happens on a daily basis in many places in the world today.]

Addendum: two links from Wired: Science, one from last night, Asteroid Impact Craters on Earth as Seen From Space,  and one from March of this year, How to Defend Earth Against an Asteroid Strike.

-Julie

http://www.unrealnature.com/