The space agency announced Thursday that its Curiosity rover had uncovered "tough" organic molecules preserved in three-billion-year-old rocks in the planet's Gale Crater, which is believed to have once contained a shallow lake.
Organic molecules were found in 3 billion-year-old sedimentary rocks near the surface.
Paul Mahaffy, director of the Solar System Exploration Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland, explained that the objective of the mission was to explore the possibility of sustaining life on Mars. Curiosity has detected large organic molecules inside ancient Martian rocks, as well as methane cycles now active on the planet.
But National Aeronautics and Space Administration scientists emphasized there could be nonbiological explanations for both discoveries made by the Curiosity rover at a site called Gale crater, leaving the issue of Martian life a tantalizing but unanswered question. Hints have been found before, but this is the best evidence yet.
While we know that Mars was habitable in the past, the case demonstrates just how hard it will be to ever prove the existence of past life on its surface.
Some geologists devote their careers to seeking organic inclusions in Earth rocks, hoping to find ancient fossils of terrestrial life. Over time, a picture of the ebb and flow of methane on Mars has emerged. Over the intervening years, fluid flowing thought it would have initiated chemical reactions that could have destroyed the organic matter - the material discovered may in fact be fragments from bigger molecules. After all, these are just organic molecules on their own, so we're still in the stage of chemistry, rather than biology.
The term "organic" means something different to a chemist than it does to a produce manager at a grocery store. The term "organic" is ambiguous - we often take it to mean "life-related" but it doesn't have to mean that.
Organic molecules are considered one of the basic building blocks of life.
"We were kind of shocked to see that with the seasons, the signal changes by a factor of three, which is a huge change and completely unexpected", says Chris Webster, a rover scientist at NASA's Jet Propulsion Laboratory.
Methane is a strong greenhouse gas, and it could have supported a climate that sustained lakes on Mars. "And the last one is geological processes, meaning the rock-forming processes themselves". Specifically, NASA says that lower levels of methane were found to decrease in the winter and peak in the summer on an annual basis. "To do that you either have to find an outcrop at the surface that has been recently exposed ... or you have to drill deep", she said.
"The question of whether life might have originated or existed on Mars is a lot more opportune now that we know that organic molecules were present on its surface at the time", wrote Utrecht University astrobiologist Inge Loes ten Kate of the Netherlands. And NASA didn't launch another mission to Mars for over a decade. Nearly exactly a year ago, NASA reported the discovery of such evidence in the form of an ancient lake that would have been suitable for microbial life to not only survive but flourish. They therefore suggest that methane could be trapped at depth, gradually seeping to the surface.