NASA’s Mars rover Curiosity has detected organic molecules in 3-billion-year-old sedimentary rocks at the base of the Murray formation at Pahrump Hills, Gale crater, as well as seasonal variations in the levels of methane in the Martian atmosphere.
Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 1,550 miles (2,500 km) from the surface of the planet. The mosaic is composed of 102 Viking Orbiter images of Mars. Image credit: NASA / JPL-Caltech.
Organic molecules contain carbon and hydrogen, and also may include oxygen, nitrogen and other elements. While commonly associated with life, these molecules also can be created by non-biological processes and are not necessarily indicators of life.
Some of the molecules identified by Curiosity include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.
“Are there signs of life on Mars? We don’t know, but these results tell us we are on the right track,” said Dr. Michael Meyer, lead scientist for NASA’s Mars Exploration Program.
Although the Martian surface is inhospitable today, there is clear evidence that in the distant past, the planet’s climate allowed liquid water to pool at the surface.
Curiosity data reveal that 3-4 billion years ago, a water lake inside Gale crater held all the ingredients necessary for life, including chemical building blocks and energy sources.
“The Martian surface is exposed to radiation from space. Both radiation and harsh chemicals break down organic matter,” said Dr. Jen Eigenbrode, a researcher at NASA’s Goddard Space Flight Center.
“Finding ancient organic molecules in the top 5 cm 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.”
To identify organic material in the Martian soil, Curiosity drilled into mudstone in 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 Curiosity’s Sample Analysis at Mars (SAM) instrument suite, 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.
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.
“Curiosity has not determined the source of the organic molecules. 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,” Dr. Eigenbrode said.
Curiosity also discovered seasonal variations in methane in the Martian atmosphere over the course of nearly three Mars years, which is almost six Earth years.
This variation was detected by the Tunable Laser Spectrometer, an instrument in Curiosity’s SAM suite.
“Water-rock chemistry might have generated the methane, but we cannot rule out the possibility of biological origins,” the researchers said.
“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 Dr. Chris Webster, a scientist at NASA’s Jet Propulsion Laboratory.
“With these new findings, Mars is telling us to stay the course and keep searching for evidence of life. I’m confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet,” concluded Dr. Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters.
The findings are published in two papers in the June 8, 2018 issue of the journal Science.
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Jennifer L. Eigenbrode et al. 2018. Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars. Science 360 (6393): 1096-1101; doi: 10.1126/science.aas9185
Christopher R. Webster et al. 2018. Background levels of methane in Mars’ atmosphere show strong seasonal variations. Science 360 (6393): 1093-1096; doi: 10.1126/science.aaq0131
This article is based on text provided by the National Aeronautics and Space Administration.
