More than four years after they were gathered, hard-to-interpret data from the Mars rover Spirit have finally been cracked. They reveal carbonate minerals to be a major component of a rock formation known as Comanche in the Columbia Hills region of the Gusev Crater.

"The discovery is significant," says Oded Aharonson, a planetary scientist at the California Institute of Technology in Pasadena who was not directly involved in the find, "because of the intimate connection between the formation of carbonates and persistent liquid water." That connection helps to solidify the view that Mars was once warm, wet and perhaps capable of supporting life.

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