Scientists say asteroid could hit Mars

By Alicia Chang

updated 11:52 a.m. ET Dec. 21, 2007

LOS ANGELES - Mars could be in for an asteroid hit.

A newly discovered hunk of space rock has a 1-in-75 chance of slamming into the Red Planet on Jan. 30, scientists said Thursday.

"These odds are extremely unusual. We frequently work with really long odds when we track ... threatening asteroids," said Steve Chesley, an astronomer with the Near Earth Object Program at NASA's Jet Propulsion Laboratory.

The asteroid, known as 2007 WD5, was discovered in late November and is similar in size to the Tunguska object that hit remote central Siberia in 1908, unleashing energy equivalent to a 15-megaton nuclear bomb that wiped out 60 million trees.

Scientists tracking the asteroid, which is halfway to Mars, initially put the odds of impact at 1 in 350 and increased the chances this week after analyzing the data. Scientists expect the odds to diminish again early next month after getting new observations of the asteroid's orbit, Chesley said.

"We know that it's going to fly by Mars and most likely going to miss, but there's a possibility of an impact," he said.

If the asteroid does smash into Mars, it'll likely aim near the equator, close to where the rover Opportunity has been exploring the Martian plains since 2004. The robot is not in danger because it lies outside the potential impact zone. Speeding at 8 miles (12.8 kilometers) a second, a collision would carve a hole the size of the famed Meteor Crater in Arizona.

In 1994, fragments of Comet Shoemaker-Levy 9 smacked into Jupiter, creating a series of overlapping fireballs in space. Astronomers have yet to witness an asteroid impact with another planet.

"Unlike an Earth impact, we're not afraid, but we're excited," Chesley said.

Initial versions of this report misstated the chances of a collision with Mars and the date of the Comet Shoemaker-Levy 9 collision.

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