Homeworld Security

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It's not all that big as asteroids go -- about the length of three football fields. But shortly after its discovery in 2004, it caused a bit of a scare. Early estimates of its orbit indicated that it could hit Earth in either 2029 or 2036, causing devastation across thousands of square miles. Astronomers named it Apophis for an Egyptian god of destruction.

It turns out that Apophis probably won't hit us after all. But it highlights the risks that Earth faces from asteroids and comets -- big chunks of rock and ice left over from the birth of the solar system. A collision with one the size of a house or bigger could kill millions.

So planetary scientists are searching for objects that could someday collide with Earth. With enough lead time, it's possible to deflect one of these objects enough to miss our planet.

The searches use telescopes in Arizona, New Mexico, Hawaii, and several other locations. They scan large regions of the sky every night. Asteroids and comets stand out because they move against the background of stars. Scientists then calculate the orbits of these objects to see if they come close to Earth.

When the first of these searches began, in the 1990s, only a few hundred Earth-approaching objects were known. Today, the number is around 5500. The searchers are cataloging everything they find that could possibly come close to Earth -- providing long-term security for our home world.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.