NASA announced two new clues in the search for life on Mars today (June 7, 2018), both discovered by its Curiosity rover. The first evidence is preserved in Martian rocks and suggests the planet could have supported ancient life. The second evidence comes from Mars’ atmosphere and relates to the search for current life on the red planet. The rover has not found evidence of life itself. But, as Michael Meyer, lead scientist for NASA’s Mars Exploration Program, said:
Are there signs of life on Mars? We don’t know, but these results tell us we are on the right track.
The new findings – of “tough” organic molecules in 3-billion-year-old sedimentary rocks near the surface, as well as seasonal variations in the levels of methane in the atmosphere – appear in the June 8 edition of the peer-reviewed journal Science.
Organic molecules are the kind of molecules you find in living things, but, as NASA was quick to point out in its statement, they:
… also can be created by non-biological processes and are not necessarily indicators of life.
Biogeochemist and geologist Jen Eigenbrode of NASA’s Goddard Space Flight Center is lead author of one of the two new Science papers, the one related to organic molecules. She said Curiosity had not determined the molecules’ source and added:
Whether it holds a record of ancient life, was food for life, or has existed in the absence of life, organic matter in Martian materials holds chemical clues to planetary conditions and processes.
Although the surface of Mars is inhospitable today, 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, including chemical building blocks and energy sources. Eigenbrode explained:
The Martian surface is exposed to radiation from space. Both radiation and harsh chemicals break down organic matter. Finding ancient organic molecules in the top five centimeters of rock that was deposited when Mars may have been habitable, bodes well for us to learn the story of organic molecules on Mars with future missions that will drill deeper.
Seasonal Methane Releases
In the second paper, scientists describe the discovery of seasonal variations in methane in the Martian atmosphere over the course of nearly three Mars years, which is almost six Earth years.
NASA said that water-rock chemistry might have generated the methane, but scientists said they can’t rule out the possibility of biological origins. 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. Chris Webster of NASA’s Jet Propulsion Laboratory is lead author of the second paper, relating to the atmospheric methane. He said:
This is the first time we’ve seen something repeatable in the methane story, so it offers us a handle in understanding it. This is all possible because of Curiosity’s longevity. The long duration has allowed us to see the patterns in this seasonal “breathing.”
Curiosity’s Sample Analysis at Mars (SAM) instrument suite was involved in both the methane discovery and the organic molecule discovery. NASA said:
To identify organic material in the Martian soil, 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 analyzed by SAM, which uses an oven to heat the samples (in excess of 900 degrees Fahrenheit, or 500 degrees Celsius) to release organic molecules from the powdered rock.
SAM measured small organic molecules that came off the mudstone sample – fragments of larger organic molecules that don’t vaporize easily. Some of these fragments contain sulfur, which could have helped preserve them in the same way sulfur is used to make car tires more durable, according to Eigenbrode.
The results also indicate organic carbon concentrations on the order of 10 parts per million or more. This is close to the amount observed in Martian meteorites and about 100 times greater than prior detections of organic carbon on Mars’ surface. Some of the molecules identified include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.
In 2013, SAM detected some organic molecules containing chlorine in rocks at the deepest point in the crater. This new discovery builds on the inventory of molecules detected in the ancient lake sediments on Mars and helps explains why they were preserved.
Finding methane in the atmosphere and ancient carbon preserved on the surface gives scientists confidence that NASA’s Mars 2020 rover and ESA’s (European Space Agency’s) ExoMars rover will find even more organics, both on the surface and in the shallow subsurface.
Bottom line: NASA’s Curiosity rover has found evidence preserved in Martian rocks, suggesting the planet could have supported ancient life. It has also found evidence in Mars’ atmosphere, relating to the search for current life on the red planet.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.