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<i>A plan to drop a quarter-tonne copper ball through Mars's atmosphere and study the ejecta it blasts away from the planet's surface on impact is to be proposed to NASA. <br /><br />The mission, called THOR, would test models suggesting the planet's tilt – and therefore its climate – swings through extreme changes every 50,000 years.<br /><br />Robotic landers and rovers have previously visited the Red Planet's equatorial regions, and an upcoming mission called Phoenix is due to touch down near the north pole in 2008. But no probe has visited the planet's mid-latitudes, where gullies and glacier-like features suggest there may be large amounts of pure water ice beneath a layer of dusty soil.<br /><br />Now, researchers led by Phil Christensen at Arizona State University in Tempe, US, are proposing a mission to search for that ice directly. The idea behind THOR (Tracing Habitability, Organics, and Resources) is to fly an observer spacecraft to Mars and, hours before it reaches the planet, release an "impactor" ball. It could be up to 230 kilograms in mass and would be aimed at a region about 40° north or south of the equator.<br /><br />The impactor, likely to be a giant copper sphere, would crash to the surface at more than 4 kilometres per second, blasting a crater about 10 metres deep. Copper is not found on Mars in large quantities - unlike iron - so when observers see it in the ejecta, they will know its from the ball and not the soil. And it is also "heavy, dense, relatively inexpensive, and easy to work with", says Christensen. The observer spacecraft would record the impact from orbit, studying the composition of the ejected soil with spectrometers.</i><br /><br />Full Story<br /><br /> <div class="Discussion_UserSignature"> <strong><font color="#3366ff">Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild.</font> - <font color="#3366ff"><em>Tennyson</em></font></strong> </div>