Mars Asteroid Stirs Concern for Earth

Jan. 2, 2008 -- It's been 100 years since a sizeable space rock smacked into Earth, leveling more than 1,200 square miles of trees in a Siberian forest. But a visceral reminder of just how much devastation an asteroid impact can have may be just around the corner.

Astronomers are keeping a close watch on a 160-foot wide asteroid designated 2007 WD5, which on Wednesday had a one in 20 chance of striking Mars on Jan. 30. Of course there are no cities or ecologies to worry about, and the prospect of Mother Nature boring a hole into the Martian terrain actually has scientists quite excited.

Scientists are on a quest to determine if Mars ever had habitats suitable for life and ultimately hope to learn if life ever evolved anywhere beyond Earth.

Three spacecraft are in orbit around Mars, including two equipped with sensors to scope out minerals. NASA has two rovers on the planet's surface as well, and a third lander slated to arrive in May, but the asteroid, if it hits at all, will leave its mark beyond the robots' range.

It would be quite another story if 2007 WD5 were heading toward Earth, as a similarly sized object did in 1908. What is believed to be a fragment from a comet plowed into the planet's atmosphere on June 30 that year and exploded over central Siberia with the force of a large nuclear bomb.

Fortunately, the region was unpopulated.

"Something of this size could take out a fairly large metropolitan area," said Donald Yeomans, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who manages the agency's Near-Earth Objects program.