Martian Claymation; December 2005; Scientific American Magazine; by George Musser; 2 Page(s)

In one of the less subtle episodes of the original Star Trek series, hippies hijack the Enterprise to get to a planet that looks like paradise but turns out to be a grim, acid-soaked purgatory. Over the past two years, a similar allegory has played itself out in Mars science. Drawn to Mars largely by signs of past Earth-like conditions, researchers have finally found definitive relics of gently lapping seas and balmier skies: in particular, deposits of sulfate salts. To form those sulfates, though, the ancient seas must have been acidic enough to burn off skin.

But a different tale is told by another class of minerals, fully mapped only recently: clays. They suggest that even before the era of the sulfates, Mars was drenched in water safe enough to dunk a hand in. "The clays indicate alteration with a lot of water," says Fran¿ois Poulet of the University of Paris-South, a member of the discovery team. "The sulfate indicates a second step in the climate of Mars."