Smash Hits

• There is evidence that, in the past, massive comets or asteroids have struck Earth’s surface. Thirty-five million years ago, a 3-kilometer ­ wide rock smashed into the ocean floor, 160 kilometers from what is now Washington, C., leaving an 85-kilometer -wi de crater buried beneath Chesapeake Bay. Another giant rock called Titan – 10 kilometers in diameter­ smashed into the Gulf of Mexico around

66 million years ago, unleashing thousands of times more energy than all the nuclear

weapons on the planet combined. “The whole Earth burned that day,” says Ed Lu, a physicist and former astronaut. Three-quarters of all life forms, including the dinosaurs, went extinct.

• Astronomers have identified numerous asteroids big enough to cause a catastrophe for the entire plane None is on course to do so in our lifetimes, but there are many smaller asteroids that could strike- with devastating effects- in the near future. On June 30, 1908, an object as big as a 15-sto ry building fell in Tunguska, a remote part of Siberia. The object­

an asteroid or a small comet-exploded several kilometers before impact, burning and blowing down trees across 2,000 square kilometers

Clouds of tiny particles of dust and ice filled the sky. The particles reflected the sun’s light onto the Earth, and for days people in Europe

could read newspapers outdoors at night. More recently, in 2013, a 20-mcter meteor exploded over Chelyabinsk Oblast, Russia, injuring dozens of people on the ground. It was the largest object to enter the Earth’s atmosphere since Tunguska.

• The next time a large object falls out of the

sky, we may be taken by surprise- though an early-warning system for near-Earth objects has recently been put into place. Sky surveys­ like the one done by Tholen – are also helping to fill the gap. “Eve1y couple of weeks,” says Lu, “we ‘ re going to be finding another asteroid Vvith, like, a one -in -a – thousand chance of hitting the Earth.”

What Can Be Done?

H Within decades , the world ‘s leaders ma y be faced with a dilemma: what to do about an incoming space object. Few experts are

giving this much  thought, according to NASA astronomer  David Morrison. 11T he number would  roughly staff a couple of shifts3 at McDonald’s,”  he says.

Ed Lu-   one of these few experts-   is working on  a plan that employs a spaceship to deflect asteroids. 11We were origina lly thinking about how you would land on an asteroid and push it,” he says. “But that doesn’t work well.” If the surface isn’t solid, you have trouble landing or

3 A shift is a group of workers who work together for a set time before being replaced by another group .

214 Unit 12B