The rock, nicknamed "Peace," is an exposure of bedrock in the hills of the Gusev Crater, where Spirit landed in January 2004.
"This is probably the most interesting and important rock Spirit has examined," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers. "This may be what the bones of this mountain are really made of. It gives us even more compelling evidence for water playing a major role for altering the rocks here," he said, according to the National Aeronautics and Space Administration's Web site.
Spirit drilled a hole about a centimeter into the rock, finding more sulfate salt than any other rock the rover has investigated, NASA said Feb. 15. Usually the sulfur has been on the surface of the rock, but the fact that it has permeated the rock means water probably had a hand in getting it there.
"Where did the salt come from? We have two working hypotheses we want to check by examining more rocks," Squyres said. "It could come from liquid water with magnesium sulfate salt dissolved in it, percolating through the rock, then evaporating and leaving the salt behind. Or it could come from weathering by dilute sulfuric acid reacting with magnesium-rich minerals that were already in the rock. Either case involves water."
Spirit also detected significant amounts of the minerals olivine, pyroxene and magnetite, all of which are common in some types of volcanic rock. The rock's texture appears to be sand-size grains coated with a material loosely binding the rock together, according to NASA.
Meanwhile, the European Space Agency's Mars Express orbiter took images of the surface of Mars that resembles ice floes at the poles on Earth, leading European scientists to speculate that an entire frozen sea is buried intact on Mars.
The scientists said Monday they believe a catastrophic event 5 million years ago sent subterranean water gushing onto the Martian surface, creating a sea. The red planet's frigid temperatures quickly turned the sea's surface to ice, which later broke up into sheets, according to National Geographic. Eventually the sea itself froze, and the entire region was later blanketed by dust, the researchers say.
Since Mars was no warmer 5 million years ago than it is today, the finding supports the possibility that water still flows underground. And liquid water brings with it the possibility of life.
The Mars rovers had already found evidence that parts of the planet were drenched in water billions of years ago. But the Mars Express images offer clues that the planet had large bodies of water in the geologically recent past, The New York Times reported.