April 8, 2002

Encounter With an Asteroid

People who enjoy worrying about asteroid catastrophes have recently been introduced to 1950 DA, a kilometer-wide chunk of rock that scientists now calculate has up to a 1-in-300 chance of smashing into the Earth, causing devastation. Fortunately, 1950 DA isn't due to arrive in our neighborhood for more than eight centuries. Our descendants should have plenty of time to find ways to cope.

The best news for people who are worried that an errant asteroid might show up any day now is that the measures being discussed to head off disaster seem blessedly benign. No need to assemble a large force of rockets carrying monstrously huge nuclear bombs to blow the asteroid off course or smash it to smithereens. That sort of scheme has always made us wonder which would be the bigger danger, the asteroids or the nuclear arsenal designed to combat them. We can be thankful that this asteroid looks as if it could be diverted by some simple changes to its surface.

It turns out that one of the big uncertainties in calculating the path of the asteroid involves how much sunlight it absorbs and then reradiates as thermal energy. Such radiation can, over the centuries, gently push the asteroid into a different orbit, much as a tiny rocket would. So if scientists in future years should conclude that a collision looks ever more likely, they can probably find ways to alter the asteroid's radiation pattern by dusting its surface with soot or powdered chalk or draping it with reflective Mylar. Such tinkering could be enough to nudge the asteroid safely away.

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