RENEE MONTAGNE, HOST:
Let's spend a few minutes contemplating life on Mars. NASA says its newest rover on Mars has found signs that the Red Planet once had conditions that would have been friendly enough to support life. The evidence comes from a scoop of grayish powder that the rover collected by drilling into a flat rock.
NPR's Nell Greenfieldboyce has more.
NELL GREENFIELDBOYCE, BYLINE: NASA's Curiosity rover is the size of a car. The robot has been driving around the bottom of a Martian crater since August, searching for proof that the planet might have once been habitable - which is not the same as actually looking for alien life.
John Grotzinger is project scientist for Curiosity at the California Institute of Technology.
JOHN GROTZINGER: You know, we're not a life detection mission. If there was microbial metabolism going on, we really wouldn't have the ability to measure that.
GREENFIELDBOYCE: But this rover can still do unprecedented things, like drill two and a half inches into some bedrock and prepare the powdery sample for analysis in its own on-board chemistry lab. And it looks like Curiosity hit pay-dirt. NASA says the rock contained some of the key chemical ingredients for life - like sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon.
It also found abundant clay minerals that suggest the rock formed at the bottom of standing water, like a lake or pond. And the watery environment wouldn't have been too salty or too acidic.
GROTZINGER: We have found a habitable environment that is so benign and supportive of life that probably, if this water was around and you had been on the planet, you would have been able to drink it.
GREENFIELDBOYCE: This wet world is long gone but just knowing it existed is a big deal. David Blake of NASA's Ames Research Center is the lead scientist for one of the rover's chemistry instruments. He says while people have speculated about places beyond Earth that might be habitable...
DAVID BLAKE: I think that is probably the only definitively habitable environment that we've described and recorded. There are places we would suggest could be habitable but we haven't measured there.
GREENFIELDBOYCE: Previous missions to Mars suggested that conditions on the planet might have been too harsh. Hap McSween is a planetary geoscientist at the University of Tennessee in Knoxville, who's worked on other Mars rover missions. He says the rover called Opportunity also found rocks that clearly had been altered by water.
HAP MCSWEEN: The problem was that the water was more like battery acid than drinking water.
GREENFIELDBOYCE: And even though some Earth microbes can survive in that kind of stew, there's debate about whether life could get its start there. The ancient water in this new discovery seems like it would be way more hospitable.
MCSWEEN: This particular water was neutral to very slightly basic, something that would not be such a challenge for organisms to live in.
GREENFIELDBOYCE: So far, Curiosity hasn't found solid evidence of the kind of organic molecules that serve as the basic building blocks for life. That's something the team will now be focusing on.
Jim Bell is a planetary scientist at Arizona State University who's working on the mission.
JIM BELL: We've got equipment that could find organic molecules and an environment where the conditions were right for habitability as we know it.
GREENFIELDBOYCE: Scientists will be out of touch with the rover for awhile in April because of the positions of Earth and Mars but they plan to drill another sample of rock in May.
Nell Greenfieldboyce, NPR News.
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