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| Space on Aug 16, 2010

David Helfand on risk from killer asteroids

An asteroid collision likely wiped out the dinosaurs. EarthSky spoke with astrophysicist David Helfand of Columbia University on the risk to people today from killer asteroids.

Many scientists believe that – more than 60 million years ago – an asteroid six miles wide struck in Mexico’s Yucatan and triggered the end of the dinosaurs. EarthSky spoke with astrophysicist David Helfand of Columbia University on the risk to people today from killer asteroids.

David Helfand: The very big ones, the ones that have global consequences, such as the one 64 million years ago that killed the dinosaurs, are very rare. They hit the Earth roughly every hundred million years or so. They do have worldwide consequences. And they will cause the extinction of a large fraction of all species on the Earth.

Dr. Helfand said that scientists today are tracking large space rocks that are potentially hazardous.

David Helfand: We are engaged in a process of systematically surveying all these rocks flying around. Of course they’re cold rocks, out there in space, and so they only shine by reflected light by the sun. And if they’re very far from Earth, that reflected signal is going to be very, very faint. Right now, the survey is pretty complete for objects larger than a kilometer in size, although there still may be a few of those out there lurking that we haven’t found yet. But for objects down to things that are say a hundred meters in size, the size of a football field or something like that, those, we’re not even close to cataloging all of them. We know in principle how to do this. It just takes lots of telescopes, lots of big cameras, and time and money.

Dr. Helfand added that tracking an asteroid is just the first step. The next step is prevention of a collision with Earth.

David Helfand: Several ideas have been proposed, such as throwing up nuclear weapons at them, or putting up a satellite that gravitationally tugs at the asteroid a little bit, so its orbit changes ever so slightly just enough to miss the Earth as it whizzes past. Those ideas are in principle doable. We understand the physics perfectly well. But they would be very expensive to implement and very little has been done to implement them.

In 2029, asteroid Apophis – about the size of a football stadium – will whisk closely past Earth. Scientists are confident it will miss, but Helfand said Apophis a good reminder that killer asteroids are out there.

David Helfand: There’s essentially zero chance of Asteroid Apophis hitting the Earth in 2029, we’ve calculated its orbit pretty precisely, and we know where its going. It’s going to miss the Earth and the moon, go between us and keep in its orbit around the sun. But it’s just, as I say, a reminder that these rocks are out there. And on a long timescale, civilization may well want to think of ways to prepare to deflect one of these, should one of them actually have Earth lined up as a target. It’s not something that people should lose sleep over when they go to bed at night. There are many other problems that the world faces that are more immediate and threatening.