Death by Asteroid?

"Eventually, our number will be up."

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Family vacation, or close call? (Steven Jurvetson/Flickr)

Nearly one million near-earth asteroids that are large enough to destroy a major city are circling through space, undetected. What's the chance that one will hit the earth?

According to former NASA astronaut Ed Lu, it's inevitable. "It's not just a theoretical construct -- it's 100 percent true that you cannot play the odds forever and win. We take a risk every day when we fly around the solar system, and eventually, our number will be up," he said during an interview at the Aspen Ideas Festival on Friday.

The last time an asteroid hit the earth and did significant damage was 105 years ago in Tunguska, Siberia, which took out an area roughly the size of the Los Angeles basin (appx. 35 miles long and 15 miles wide). "Those happen about every 200 years, so in this century, there's about a 30 percent chance we'll see another one," Lu warned.

If the possibility of death by asteroid doesn't charm, perhaps death by comet will do the trick. Harvard physicist Lisa Randall is working on a theory of dark matter in the universe, which might be able to disrupt the path of comets, she says. "There's a lot of evidence that most of the dark matter doesn't interact [with light]. So we hypothesize that there could be some small point that interacts. Now that's very interesting, because just the way that we have a milky way disk inside a halo of dark matter... maybe you also have a disk of dark matter. If that's true, it turns out it could have extremely interesting consequences. I'm not going to lie -- this is very speculative. But what happens is, it would affect the solar oscillations through the galaxy, and as a consequence of that... the gravitational pull from this dark disk could actually displace comets in a way that actually creates craters on earth."

Randall and Lu, along with Fermilab astrophysicist Craig Hogan, went on to outline many interesting questions that remain in experimental and theoretical physics, including what dark matter is exactly and why the amount of dark matter in the universe is so similar to the amount of normal matter (about six times as much). But a more pressing question remains: should we all worry about the impending asteroid that will render us, as moderator Bridget Kendall put it, "dinosaur toast"?

"I'm not saying it's the pressing threat that we need to solve today, but it is pressing in that we don't know when the next one's coming," said Lu.