You know this: Earth's oceans are littered with floating pieces of broken ships, busted piers, waterlogged sofas, styrofoam cups, and lost frisbees. Oceangoing vessels beware: a big piece of debris might rip a hole in your hull while a small piece of garbage might snap your rudder.

You also know this: near-Earth orbital space is filled with spent rocket stages, broken satellites, and lost hammers and screws. Satellites beware: a collision could rip a hole in your antenna or catastrophically bust you to smithereens.

But do you know this? Our solar system is chock full of the flotsam and jetsam left over from the birth of the Sun and her large planets. These smallest members of our solar system, the comets and asteroids, can periodically pass through Earth's neighborhood. Some of them have already collided with Earth; there's plenty more to come. Earth beware: these high-speed collisions could produce a meteor shower—shooting stars; a bright fireball in the sky—as we witnessed over the Chelyabinsk region of Russia this February; a hole in the ground—like the Barringer meteor crater in Arizona; or global mass extinction—as many scientists think happened 65 million years ago after a 10-km diameter rock fell from the sky and dug a 100-km- wide hole in the Yucatan Peninsula near the modern town of Chicxulub.

The statistical likelihood that human civilization will be wiped out any time soon by a global catastrophe triggered by the impact of a comet or asteroid with the Earth is exceedingly but not vanishingly small; however, the chances are close to 100 percent that sometime in the next five millennia a football-stadium-sized asteroid will punch through our atmosphere and dig a hole in the ground as big as downtown San Francisco, or explode a few miles up in the atmosphere, sending out shock waves and lighting fires across hundreds of miles. Are we ready? Should we get ready? Can we be ready?

Donald Yeomans thinks we can and should get ready—and that now is the time to begin working feverishly toward these goals. As he notes in Near-Earth Objects, we are off to a good start. Astronomers know how to find these objects; all you need to do is provide them with the funding to build the right telescopes and allow them to do their work. NASA, working with astronomers like Yeomans, has a set of protocols in place for flagging space objects that are potentially dangerous and estimating the likelihood of a future collision, including the day, year, latitude, and longitude when and where said object will strike the Earth. What we're not so good at yet is doing anything to mitigate the potential risks associated with that future doomsday.

The sky is falling, but the big pieces are more likely to fall on the heads of my great-great-grandchildren than on my own bald head. I think we have plenty of time to identify all the near-Earth objects and develop methods for protecting ourselves, while Yeomans would like to see us invest more resources into working on this problem sooner rather than later. Yeomans and I agree, however, that more people should understand that Chicken Little was right, and that we can do quite a bit to limit the damage that is inevitable if we choose to do nothing.

David A. Weintraub is professor of astronomy at Vanderbilt University.

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