Unwelcome visitors

So you're out there lying in the yard on your back, a sunny afternoon in July, gazing lazily up at the sky. An occasional plane flies overhead. A few blue jays flit around. Then far above you see a speck -- gosh, is that an eagle?

The speck gets larger and larger. Soon, it's as big as the moon. It's as big as a house. Now you see that it's irregular in shape, like a big rock. Like a huge boulder. But it keeps filling more and more of the sky. You let out a yell. You want to run, but there's no place to run. It's coming right at you, and it keeps getting larger.

If you're a scientist, perhaps your last thought on earth might be a quick calculation that this odd object is impossibly big -- it's at least seven miles wide. And then you're dead. But you weren't particularly unlucky among all mankind, just because your backyard happened to fall within the seven-mile impact zone. Because within a short time, every other human being on earth -- even those in China -- would also be dead.

Dead though you might be, you would have had the privilege of observing the same sight that an observant dinosaur reclining on a beach in the Yucatan would have observed about 65 million years ago. The impact of an asteroid, seven miles or so in diameter, resulting in the Chicxulub crater off the northern coast of the Yucatan peninsula, was sufficient to have triggered world-wide earthquakes, volcanic eruptions and tidal waves. Enormous quantities of dust and the release of large amounts of carbon dioxide and sulfate aerosols would have resulted in dramatic planetary cooling and acid rain, wiping out or severely disrupting significant portions of the food chain.

Most scientists believe that the impact that resulted in the Chicxulub crater, either by itself or in concert with impacts from other asteroids, resulted in the extinction of the dinosaurs -- the largest animals inhabiting the earth at the time.

In an interesting article in this week's New Yorker, Tad Friend describes efforts by the scientific community to monitor the orbits of known asteroids and comets, in the hope that a similar disaster in the future can somehow be averted. Their efforts, however, remind me of efforts to find better tools to diagnose prostate cancer -- once you've identified the problem, the question becomes what do you do about it?

In 2005, scientists smashed a rocket at 23,000 mph into a passing comet, just to see how much its orbit would be deflected. The answer was -- none at all. No more than firing a bullet at a semi truck speeding on the freeway would shove it off onto the shoulder. And you can't blow a comet or asteroid to smithereens -- that would merely convert a speeding object into a speeding shower of rather large smithereens heading directly at you at tremendous speed.

And yet, if we had even ten years' advance warning of a probable impact, and could change the velocity of the threatening orbital object by just one centimeter per second, we could cause its orbit to change sufficiently over that period of time to avoid the threat to the earth.

One problem that scientists face is the large amounts of money required for accurate advance detection of those orbits posing a risk to the earth. Another problem is the even larger amounts required to meet the danger once detected. And as one scientist quoted in the article noted, American rocket technology has reverted back to where it was in the 1960's.

We all know about the Tunguska explosion over Siberia in 1908, probably caused by a meteor well under a hundred yards in diameter. The explosion in the atmosphere was one thousand times as powerful as the Hiroshima bomb. In 2002, an asteroid exploded over the Mediterraean, and another object hit a mountain in Siberia the same year. In 2008, an asteroid the size of a truck hit the desert in Sudan. In 2009, another one exploded over Indonesia with three times the force of a Hiroshima bomb.

So far we've been lucky. None of these impacts and explosions has been over a city or densely populated area. Even if it had, although it would have been an incalculable disaster, it would not have destroyed humanity. We're used to war and we're used to disasters. With so many problems in the world, it's hard for a government to commit vast amounts of money in an attempt to prevent "limited" potential disasters of this sort, and it's hard for anyone to worry about total annihilation of our species when extinction of the dominant species hasn't occurred for the past 65 million years. Money is scarce. If an asteroid or comet large enough to destroy life on earth hasn't hit us in 65 million years, we tend to rationalize, why should we worry about the next hundred years?

Maybe our hypothetical dinosaur himself had been thinking along those lines as he lay on the beach -- just before he noticed a large speck growing ever larger in the sky.