From previous Mars missions, we’ve learned that Martian rocks and soil contain minerals that form in liquid water. This is evidence that liquid water once existed on the Martian surface in the ancient past. However, these particular minerals indicate that the water was very acidic. Not a very hospitable environment for forms of life that exist on planet Earth. Did Mars ever have environmental conditions that would have made it habitable for life as we know it?
Spacecraft in orbit around Mars have detected, in a location called Gale Crater, layers of rock that have the signature of clay minerals that form in “normal” water. This is the why Gale Crater was selected as the landing destination of the Curiosity Rover. A safe landing site for the rover was several miles away from the layers of interest. So, scientists knew it would be at least a year before Curiosity reached the particular rock layers of interest. Probing those layers for evidence of a past habitable environment was not expected to occur quickly. However, in September 2012, not far from its landing site, Curiosity unexpectedly found evidence of an ancient stream bed. In December, Curiosity drove into a different type of terrain. Then, in early February, Curiosity used a drill carried at the end of its robotic arm to bore into an interesting rock and collect a sample from the rock’s interior.
When the sample was analyzed by instruments on board the rover they found the presence of clay minerals that form in normal pH water. The rover will next analyze a second sample to confirm the findings. So, much earlier than expected, the Curiosity Rover has found evidence that Mars once had a habitable environment! For more detailed information, see the Press Release on NASA’s Curiosity Rover website.