From Nature:
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. 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.
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