The sample that was analyzed came from Gale Crater, near the site where Curiosity landed on Aug. 6, 2012, and discovered an ancient streambed in September. The sedimentary rock that was part of an ancient streambed descending from the rim of Gale Crater contained carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, all of which play important roles in lifeforms on Earth.
“A fundamental question for this mission is whether Mars could have supported a habitable environment. From what we know now, the answer is yes,” said Michael Meyer, lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington, DC.
“Clay minerals make up at least 20 percent of the composition of this sample,” said David Blake, principal investigator for the CheMin instrument at NASA's Ames Research Center in Moffett Field, Calif.
The Chemistry and Mineralogy (CheMin) and Sample Analysis at Mars (SAM) systems onboard the Curiosity rover indicate that the Yellowknife Bay area currently being explored by the rover was once at the end of either an ancient river system or an intermittently wet lacustrine environment. The bedrock in the area is fine-grained mudstone that shows evidence of multiple periods of intermittently wet conditions, including nodules and veins. This ancient wet environment, unlike some others on Mars, was not strongly acidic, very salty, or lacking in chemical gradients.
The rocks in the area contain clay minerals, as well as sulfate minerals. The presence of calcium sulfate indicates neutral or mildly alkaline pH, in the 7-8 range. The clay minerals result from fresh water mixing with igneous minerals. There is also a gradient of oxidized, less-oxidized, and a small amount of non-oxidized chemicals, which could have provided an energy source for microorganisms. This electrochemical gradient was first hinted at when the drill cuttings were revealed to be gray rather than red.
“The range of chemical ingredients we have identified in the sample is impressive, and it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for micro-organisms,” said Paul Mahaffy, principal investigator of the SAM suite of instruments at NASA's Goddard Space Flight Center in Greenbelt, Md.
“We have characterized a very ancient, but strangely new 'gray Mars' where conditions once were favorable for life. Curiosity is on a mission of discovery and exploration, and as a team we feel there are many more exciting discoveries ahead of us in the months and years to come,” said John Grotzinger, Mars Science Laboratory project scientist at the California Institute of Technology in Pasadena, Calif.
Observations will continue to be made in the Yellowknife Bay area for several months before the rover is driven to Mount Sharp, the central mound inside Gale Crater. There, scientists will study the layers of minerals that are exposed, which may provide more information about the diversity and duration of habitable environmental conditions.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Curiosity project for NASA's Science Mission Directorate in Washington, DC.