The more we learn about Mars, the more it seems that the red planet once could have harbored life.
"We really can't tell if this methane we see today is a current product of serpentinization [a chemical reaction between iron-bearing rocks and liquid water] or microbial activity at some depth", says Michael Mumma, the NASA Goddard scientist who discovered Mars's methane plumes. Organic matter can be one of several things: a record detailing ancient life, a food source for life or something that exists in the place of life. Yet over the course of 55 Earth months (three Martian years), Webster and his team were able to use SAM to detect tiny, regular patterns in which methane-natural gas-increased from 0.24 to 0.65 parts per billion at the end of northern Mars' summer. Curiosity reports that methane levels on Mars go up and down in a predictable cycle.
Here on Earth, 95 percent of all methane molecules are the product of living chemistry. On Mars, that's been a maddening challenge: While scientists have detected bursts of methane on the planet, they've appeared at random - and thus, it's been hard to figure out what the source is. It could be. Organic molecules are the building blocks of all known forms of life.
More powerful spacecraft are needed to prove whether life ever existed on Mars.
The organic-rich sample came from the bottom of what used to be a massive lake inside Gale Crater billions of years ago. She pointed out that the surface of Mars is regularly exposed to space radiation, and that radiation and chemicals typically break down organic matter.
The organic molecules preserved in 3 billion-year-old bedrock suggest conditions at Mars may have once been conducive to life. Curiosity sampled mudstone in the top 5 centimeters from the Mojave and Confidence Hills localities within Gale Crater.
"Curiosity has not determined the source of the organic molecules", Eigenbrode said in the release.
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Curiosity, which has been exploring Gale Crater since it landed in 2012, has previously dug up signs of organic molecules in the ancient lakebed, by taking rock samples and subjecting them to the suite of laboratory instruments in its belly.
For his part Webster says he has no preference among the different explanations, and believes it will take a long time before any final conclusions can be drawn. This is close to the amount observed in Martian meteorites and about 100 times greater than prior detections of organic carbon on Mars' surface.
But NASA managers say the new discoveries show the agency's Mars exploration plans are on the right track.
It successfully tested a new drilling method in May on the Red Planet, making a 50-millimetre deep hole in a target called "Duluth".
Webster and his colleagues suspect that the methane comes from deep underground, and temperature swings on Mars's surface throttle its flow upward.
As winter falls, gases are once again trapped in ice cages, helping explain at least some of the vanishing methane.
The discovery is not a direct evidence of life.
"And maybe we can find something better preserved than that, that has signatures of life in it", she told AFP.