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Mars Attack!

January 27, 2006 By Mark Peplow This article courtesy of Nature News.

Red planet under fire in proposed mission.

Scientists have had a smashing idea that could help them explore beneath Mars's dusty surface. Slamming a hefty chunk of copper into the planet should excavate enough material to reveal water ice or carbon-based chemicals lurking underground, according to a proposed NASA mission.

The idea follows the success of Deep Impact, a mission that fired a copper 'impactor' into comet Tempel 1, while its delivery craft recorded the whole show with an array of sensors (see ' Deep Impact: sifting through the debris').

The new mission takes exactly the same approach to Mars. Called THOR (Tracing Habitability, Organics and Resources), it would be the second of NASA's Mars scout missions, low-cost probes that are designed and built in just a few years. The first scout, Phoenix, is due to launch in August 2007.

THOR has been proposed by Phil Christensen, a planetary scientist at Arizona State University, Tempe, and David Spencer of the Jet Propulsion Laboratory in Pasadena, California.

Christensen estimates that the impactor should be about 100 kilograms or so, and hit the planet at more than 15,000 kilometres per hour. It is hoped this would make a crater roughly 50 metres in diameter, and up to 25 metres deep.

Meanwhile, its mother ship would look for ice, minerals and organic compounds thrown out by the crash.

A cunning plan

Christensen admits that it is a simple enough approach. "I guess there'll be a lot of people out there going, 'Why didn't I think of that'," laughs Christensen. But that simplicity should help to ensure the mission's success, he adds.

Keeping two rovers running around on Mars is a tremendous feat of engineering, but sending something that can burrow or drill is even more challenging, Christensen points out.

Moreover, exploring icy parts of the surface by rover carries the risk that a robot may accidentally seed a site with earthly life. Such a craft could generate enough heat to melt the ice, providing a miniature habitat for microbes.

An explosion of copper is so violent that it neatly avoids that risk, explains Christensen: "It's completely self-sterilizing."

High hopes

The two investigators have a good track record for similar missions. Christensen already has four scientific instruments on or around Mars, and Spencer was mission manager for Deep Impact. Together they think they have a good shot at winning the go-ahead for their proposal. NASA scout missions are selected from a large pool of ideas in a knockout competition.

"We've made it through the first couple of rounds," says Christensen. This summer he and Spencer will go up against about 15 other proposals, after which three or four will be worked up into detailed mission plans. If THOR gets the nod, they plan to launch in 2011.

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