MAGNETS of varying strengths mounted on the Pathfinder lander could reveal whether the surface of Mars was awash with water for much of its history.
The vista revealed by Pathfinder鈥檚 camera supports the theory that the area where the spacecraft landed was the site of a huge, ancient flood. Some scientists believe the young Mars was shrouded in a thick atmosphere and had liquid water on its surface for millions of years. But others think that the floods, when they came, were shortlived-perhaps brought on by a freak heating of the planet鈥檚 permafrost by collisions with asteroids or comets.
Jens Martin Knudsen, a physicist at the Niels Bohr Institute in Copenhagen, believes the answer may lie in the planet鈥檚 dusty soil. 鈥淲e still don鈥檛 know how or when this soil formed,鈥� he says. The dust鈥檚 colour suggests that it is an iron oxide, or rust, as did experiments on the Viking landers in which the dust was attracted to strong magnets.
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Knudsen suspects that the dust may hold a magnetic memory of the Red Planet鈥檚 watery past. If water covered much of the surface for a long period, he says, iron from the rock would have combined very slowly with Mars鈥檚 scarce oxygen. That would have led to the production of strongly magnetic oxides such as magnetite and maghemite. In addition, if the dust formed after long contact with water it would be pure iron oxide, whereas if it formed by the interaction between oxygen and dry rock it would also contain elements such as titanium.
Knudsen鈥檚 team built three credit card-sized magnetic arrays, which are positioned on each of Pathfinder鈥檚 two ramps and the main lander. Each array contains a series of five magnets of decreasing strength, so the researchers can calculate the magnetic strength of the dust by noting where it settles. The weakest magnet was chosen so that it will just hold onto the most strongly magnetic maghemite dust.
Only a tiny trace of dust appeared on the strongest magnet in Pathfinder鈥檚 first week on Mars-too little to draw any conclusions yet. None had settled on any of the weaker magnets. But once dust has accumulated to a sufficient depth, the magnets on the ramps could be visited by the Sojourner rover, which could use its alpha proton X-ray spectrometer to investigate the chemical composition of the dust.
