Elizabeth Rusch - Impact!: Asteroids and the Science of Saving the World

A chair-size chunk of the Chelyabinsk asteroid busted a hole through the thick ice of Lake Chebarkul.

A clue about what really happened lay more than fifty miles (80 km) away in the middle of a frozen lake in the Siberian wilderness. People nearby had followed the ball of light as it soared across the sky. They trudged across the snow-covered ice until they came to an eerie sight: a twenty-foot-wide (6 m) round hole in the thick ice. As they peered into the dark water, someone joked: Now green men will crawl out and say hello.

No aliens sprang from the hole, but the locals were rightthe flash and blasts were caused by an object from outer space. An asteroid the size of a six-story building and heavier than the Eiffel Tower had careened toward Earth and exploded in the sky. The largest piece left, about the size of a chair, had landed on the bottom of the lake. Thousands of smaller pieces littered the ground for miles.

No one saw the Chelyabinsk asteroid coming, yet scientists have a good idea of how it got there. Most asteroids that approach Earth come from the main asteroid belt, an area where millions of the huge space rocks orbit the sun between Mars and Jupiter.

These two fragments of the Chelyabinsk meteorite were found in a field between two villages outside the city. The broken fragment shows a light-colored interior and the dark fusion crust formed during the rocks fiery journey though the atmosphere. The unbroken fragment on the right shows a complete fusion crust.

Asteroids in the belt between Mars and Jupiter generally stay there for billions of years. But sometimes an asteroid is bumped out of the belt by the gravitational pull of objects around it, from a collision, or even from the pressure of sunlight on its surface. When this happens, the asteroids orbit becomes unstable and it can begin to swing near Earth. Within a few million years, most near-Earth asteroids will do one of three things: crash into the sun; get pushed out of the solar system; or crash into a planet, perhaps Earth.

THANK YOU, ATMOSPHERE!

The Earth is getting pummeled by small fragments of asteroids all the time, and most of the time no one notices. Thats because the atmosphere does a really good job protecting us.

How does something so light and airy protect us? The atmosphere is a layer of gases around the planet, held in place by gravity. When an asteroid comes screaming through the atmosphere, the gases compress around it quickly, heating and incinerating the object. The atmosphere is like a giant laser, blasting apart anything that flies fast into it.