17th December 2014

Possible hints of organic life on Mars

NASA reports detecting an unusual increase, then decrease, in the amounts of methane in the atmosphere of the planet Mars, as well as Martian organic chemicals in powder drilled from a rock by the Curiosity rover.

This image illustrates possible ways methane might be added to Mars' atmosphere (sources) and removed from the atmosphere (sinks). The Curiosity rover has detected fluctuations in methane concentration in the atmosphere, implying both types of activity occur on modern Mars. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

NASA's Mars Curiosity rover has measured a tenfold spike in methane, an organic chemical, in the atmosphere around it and detected other organic molecules in a rock-powder sample collected by the robotic laboratory’s drill.

"This temporary increase in methane – sharply up and then back down – tells us there must be some relatively localised source," said Sushil Atreya of the University of Michigan, Ann Arbor, and Curiosity rover science team. "There are many possible sources, biological or non-biological, such as interaction of water and rock."

Researchers used Curiosity’s onboard Sample Analysis at Mars (SAM) laboratory a dozen times in a 20-month period to sniff methane in the atmosphere. During two of those months, four measurements averaged seven parts per billion. Before and after that, readings averaged only one-tenth that level.

Curiosity also detected different Martian organic chemicals in powder drilled from a rock dubbed Cumberland, the first definitive detection of organics in surface materials of Mars. These Martian organics could either have formed on Mars or been delivered to Mars by meteorites.

Organic molecules, which contain carbon and usually hydrogen, are chemical building blocks of life, although they can exist without the presence of life. Curiosity's findings from analysing samples of atmosphere and rock powder do not confirm whether Mars has ever harboured living microbes, but the findings do shed light on a chemically active modern Mars and on favourable conditions for life in the ancient past.

"We will keep working on the puzzles these findings present," said John Grotzinger, project scientist at the California Institute of Technology. "Can we learn more about the active chemistry causing such fluctuations in the amount of methane in the atmosphere? Can we choose rock targets where identifiable organics have been preserved?"

The researchers worked for many months to determine whether any of the organic material detected in the Cumberland sample was truly Martian. Curiosity’s SAM lab detected in several samples some organic carbon compounds that were, in fact, transported from Earth inside the rover. However, extensive testing and analysis yielded confidence in the detection of Martian organics.

The SAM analysed hydrogen isotopes from water molecules that had been locked inside a rock sample for billions of years and were freed when SAM heated it, yielding information about the past history of Martian water. The ratio of a heavier hydrogen isotope – deuterium – to the most common hydrogen isotope can provide a signature for comparison across different stages of a planet's history.

"It's really interesting that our measurements from Curiosity of gases extracted from ancient rocks can tell us about loss of water from Mars," said Paul Mahaffy, SAM principal investigator and lead author of a report published this week by the journal Science.

Click to enlarge

Cross-bedding seen in the layers of this Martian rock is evidence of water movement recorded by the waves or ripples of loose sediment the water passed over, such as a current in a lake. This image was acquired by the Mastcam on NASA's Curiosity Mars rover last month.

The ratio of deuterium to hydrogen has changed because the lighter hydrogen escapes from the upper atmosphere of Mars much more readily than heavier deuterium. In order to go back in time and see how the deuterium-to-hydrogen ratio in Martian water changed over time, researchers can look at the ratio in water in the current atmosphere and water trapped in rocks at different times in the planet’s history.

Martian meteorites found on Earth also provide some information, but this record has gaps. No known Martian meteorites are even close to the same age as the rock studied on Mars, which formed about 3.9 billion to 4.6 billion years ago, according to Curiosity’s measurements.

The ratio that Curiosity found in the Cumberland sample is about one-half the ratio in water vapour in today's Martian atmosphere, suggesting much of the planet's water loss occurred since that rock formed. However, the measured ratio is about three times higher than the ratio in the original water supply of Mars. This suggests much of Mars' original water was lost before the rock formed.

Curiosity is one element of NASA's ongoing research and preparation for human exploration of Mars in the 2030s. Other upcoming missions include the InSight drilling probe in 2016, another Curiosity-style rover in 2020 and a sample return mission in 2023.

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