Powder from inside a “mudstone” that was the first rock on another planet ever drilled for samples demonstrates that Mars was once habitable, confirming what planetary scientists have long suspected.

The gray powder drilled from a sedimentary rock on the floor of Gale Crater, where the nuclear-powered Curiosity rover has been exploring since landing there last summer, was analyzed by a pair of robotic chemistry labs inside the rover body. They found sulfur, nitrogen, hydrogen, oxygen, phosphorous and carbon — all chemical ingredients for life as we know it on Earth and a major target of the $2.5 billion Mars Science Laboratory (MSL) mission.

The sample also contained clays produced when “relatively fresh water” reacted with olivine and other igneous minerals, and calcium sulfate, which suggests the sample material is neutral or mildly alkaline.

“We have found a habitable environment that is so benign and supportive of life that if this water had been around and you had been on the planet, you would have been able to drink it,” said John Grotzinger, the MSL project scientist.

Grotzinger estimated that the material analyzed is ancient — “older than 3 billion years” — but with Curiosity’s instruments it is difficult to determine if it is relatively recent material from the alluvial fan that has washed down from the 5.5-km-high central mountain, or the base of the mountain itself.

“It’s about the time we start seeing the first record of life preserved on Earth,” he said.

Plans call for Curiosity to drill one or two more rock samples in Yellowknife Bay to confirm its findings before starting for the central mountain — designated Mt. Sharp by JPL controllers after a late colleague — that rises in the center of Gale Crater. Collecting those next samples will have to wait until the end of April, while Mars passes behind the Sun and out of communication with Earth, and the prospects for discovery at the mountain are enticing.

“We’re actually not quite sure how Mt. Sharp was built,” said Michael Meyer, lead scientist for NASA’s Mars exploration program. “The real evidence of how that happened is in Mt. Sharp … we have to go to Mt. Sharp to see those layers to sort that out.”