Track a falling star

the "shooting stars" or meteors that streak through our atmosphere are actually very old objects. They have typically travelled for millions of years before they hit the Earth. Now scientists have developed a new model that explains why they take so long to come to the Earth. It was believed that the meteors are produced when asteroids collide. These collisions throw some fragments into special zones from where they are kicked by the gravity of Jupiter and Saturn till they ultimately hit the Earth a few million years later. This theory has a problem because some of the meteors studied have ages of tens of millions of years.

Now scientists in Prague have developed a computer model that simulates the birth and evolution of meteors. In their model, the meteoroid creating collisions occur deep inside the asteroid belt. Then, a slow but steady force pushes the rocks toward a gravitational "escape hatch" which allows them to escape from the asteroid belt. The force, called the Yarkovsky effect, arises when the sun-warmed face of the spinning rock turns away from the sun. As the warm face cools, the escaping radiation nudges the tumbling stone. The entire trip takes about 10 million years, which matches the estimates of the oldest meteors found on Earth ( Nature , October 5, 2000).

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