Mars Discovery: No Little Green Men but - Finally - Lots of Carbonate

Four years after the rover Spirit visited the "Columbia Hills" region of Mars's Gustave Crater, scientists are reporting the discovery of rocks containing carbonate minerals.

This has created a stir in scientific circles with researchers long eager to find large concentrations of carbonate, hoping it will provide clues to the red planet's early history and perhaps, shed light on whether Mars once hosted life forms. Though small amounts of carbonate have been found, this is the first time the mineral has been discovered in large outcrops of rock.

The rocks in question are about 25 percent carbonate by weight. Their existence was reported in the online edition of the journal Science. For more, check out Emily Lakdawalla's fine blog explaining this in some detail.