[ExI] Asteroid on track for possible Mars hit

[Amara Graps]

http://www.latimes.com/news/science/la-sci-mars21dec21,0 
6729483.story?coll=la-home-center

>From the Los Angeles Times

Asteroid on track for possible Mars hit
Researchers say the object, about 160 feet across, has an
unusually good chance of plowing into the planet Jan. 30.

By John Johnson Jr.
Los Angeles Times Staff Writer

December 21, 2007

Talk about your cosmic pileups.

An asteroid similar to the one that flattened forests in Siberia
in 1908 could plow into Mars next month, scientists said Thursday.

Researchers attached to NASA's Near-Earth Object Program, who
sometimes jokingly call themselves the Solar System Defense Team,
have been tracking the asteroid since its discovery in late
November.

The scientists, based at the Jet Propulsion Laboratory in La
CaÒada Flintridge, put the chances that it will hit the Red Planet
on Jan. 30 at about 1 in 75.

A 1-in-75 shot is "wildly unusual," said Steve Chesley, an
astronomer with the Near-Earth Object office, which routinely
tracks about 5,000 objects in Earth's neighborhood.

"We're used to dealing with odds like one-in-a-million," Chesley
said. "Something with a one-in-a-hundred chance makes us sit up
straight in our chairs."

The asteroid, designated 2007 WD5, is about 160 feet across, which
puts it in the range of the space rock that exploded over Siberia.
That explosion, the largest impact event in recent history, felled
80 million trees over an area of 830 square miles.

The Tunguska object broke up before hitting the ground, but the
Martian atmosphere is so thin that an asteroid would probably
plummet to the surface, digging a crater half a mile wide, Chesley
said.

The impact would probably send dust high into the atmosphere,
scientists said. Depending on where the asteroid hit, such a plume
might be visible through telescopes on Earth, Chesley said.

The Mars Reconnaissance Orbiter, which is mapping the planet,
would have a front-row seat. And NASA's two JPL-built rovers,
Opportunity and Spirit, might be able to take pictures from the
ground.

Because scientists have never observed an asteroid impact -- the
closest thing being the 1994 collision of comet Shoemaker-Levy
with Jupiter -- such a collision on Mars would produce a
"scientific bonanza," Chesley said.

The asteroid's course has now taken it behind Earth's moon, he
said, so it will be almost two weeks before observers get another
chance to plot its course more accurately.

The possibility of an impact has the Solar System Defense Team
excited.

"Normally, we're rooting against the asteroid," when it has Earth
in its cross hairs, Chesley said. "This time we're rooting for the
asteroid to hit."

john.johnson at latimes.com

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Amara Graps, PhD      www.amara.com
Research Scientist, Southwest Research Institute (SwRI), Boulder, Colorado