What Happens If An Asteroid Hits Mars?

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Published January 07, 2008

| Space.com

The possibility of an asteroid walloping the planet Mars this month is whetting the appetites of Earth-bound scientists, even as they further refine the space rock's trajectory.

The space rock in question — Asteroid 2007 WD5 — is similar in size to the object that carved Meteor Crater into northern Arizona some 50,000 years ago and is approaching Mars at about 30,000 miles per hour (48,280 kph).

Whether the asteroid will actually hit Mars or not is still uncertain.

Such an impact, researchers said, would prove an awesome blow for planetary science since NASA's Mars Reconnaissance Orbiter (MRO) and a flotilla of other spacecraft are already in position to follow up any impact from orbit.

"An impact that we could witness/follow-up with MRO would be truly spectacular, and could tell us much about the hidden subsurface that could help direct a search for life or life-related molecules," said John Rummel, NASA's senior scientist for astrobiology at the agency's Washington, D.C., headquarters.

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Observations of the asteroid between Dec. 29 and Jan. 2 allowed astronomers to slightly lower the space rock's odds of striking Mars to about 3.6 percent (down from 3.9), giving the object a 1 in 28 chance of hitting the planet, according to Tuesday report from NASA's Near Earth-Object program office at the Jet Propulsion Laboratory in Pasadena, Calif.

More observations may further reduce the asteroid's impact chances to nil, NEO officials said. The space rock's refined course stems from observations by astronomers at New Mexico Tech's Magdalena Ridge Observatory.

But if WD5 does smack into Mars, some astronomers have a fair idea of what havoc it may spawn. The likely strike zone would be near the equator, but to the north of the current position of NASA's Opportunity rover at Victoria Crater, NASA officials have said.

Mark Boslough, a collision dynamics expert at New Mexico's Sandia National Laboratory, said the atmosphere at Mars' surface is similar to that of Earth at an altitude of 12 miles (20 km). Some space rocks that target Earth explode under the pressure created as they stream into our atmosphere. But they tend not to explode until much below the 12-mile mark.

"So this won't be an airburst," Boslough said. "It will either hit the ground intact and make a single crater, or break up and generate a cluster of craters."

The collision, were it to occur, could also create a visible dust plume as ejecta is lofted high into the martian atmosphere, he said.

The resulting crater could reach more than a half-mile (0.8-km) in diameter, or about the size of the Opportunity rover's Victoria home, NASA added.

Boslough's break-up scenario is reminiscent of Comet P/Shoemaker-Levy 9, which broke into more than 20 fragments as it neared Jupiter in 1994, then repeatedly pummeled the gas giant over the course of six days.

The resulting impact scars were visible to telescopes on Earth, in orbit and NASA's Galileo probe, which was circling Jupiter at the time of the collision.

Like Galileo at Jupiter, NASA's MRO probe and its High-Resolution Imaging Experiment (HiRISE) camera would be in prime position for a martian collision. With its ability to resolve objects three feet (one meter) across, HiRISE as been billed as the most powerful camera ever sent to study Mars.

"If the asteroid hits Mars, we'll get a great look at the crater within a few days of impact," said HiRISE principal investigator Alfred McEwen of the University of Arizona's Lunar and Planetary Laboratory in Tucson.

SPACE.com Staff Writer Tariq Malik contributed to this report from New York City.

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