Signs of life on Mars

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NASA’s Curiosity rover has discovered ancient organic molecules on Mars, embedded within sedimentary rocks that are billions of years old. Photo: NASA/GSFC

NASA’s Curiosity rover has found new evidence preserved in rocks on Mars that suggests that the planet could have supported ancient life. It has also found evidence for methane in the Martian atmosphere that could hold a clue for current life on the red planet.

The new findings, which include “tough” organic molecules in three-billion-year-old sedimentary rocks near the surface and seasonal variations in the levels of methane in the atmosphere, have been published as two papers in the June 8 issue of “Science”.

While commonly associated with life, organic molecules, which contain carbon and hydrogen and may also include oxygen, nitrogen, and other elements, can also be created by non-biological processes and are not necessarily indicators of life.

“With these new findings, Mars is telling us to stay the course and keep searching for evidence of life,” said NASA’s Thomas Zurbuchen. “Curiosity has not determined the source of the organic molecules,” said Jen Eigenbrode of NASA’s Goddard Space Flight Centre, the lead author of one of the two “Science” papers.

Thus, there is clear evidence that in the distant past, the Martian climate allowed liquid water, an essential ingredient for life as we know it, to pool at the surface. Data from Curiosity reveal that billions of years ago a water lake inside Gale Crater held all the ingredients necessary for life.

Curiosity drilled into sedimentary rocks known as mudstone from four areas in Gale Crater. This mudstone gradually formed billions of years ago from silt that accumulated at the bottom of the ancient lake. The rock samples were analysed by Curiosity’s Sample Analysis at Mars (SAM) instrument.The results also indicate organic carbon concentrations on the order of 10 ppm or more. This is close to the amount observed in Martian meteorites and about 100 times greater than earlier detections of organic carbon on Mars. The second paper describes the discovery of seasonal variations in methane in the Martian atmosphere over the course of nearly three Mars years (almost six Earth years). This variation was also detected by SAM.

Water-rock chemistry might have generated the methane, but the possibility of biological origins cannot be ruled out. Methane previously had been detected in Mars’ atmosphere in large, unpredictable plumes. This new result shows that low levels of methane within Gale Crater repeatedly peak in warm, summer months and drop in the winter every year. “This is the first time we’ve seen something repeatable in the methane story, so it offers us a handle in understanding it,” said Chris Webster, the lead author of the second paper.