According to a new NASA lab experiment, rovers may have to dig about two meters or more below the Martian surface to find signs of ancient life, because ionizing radiation from space breaks down small molecules like amino acids relatively quickly.
Amino acids can be made by life and by non-biological chemistry. However, finding certain amino acids on Mars would be considered a potential sign of ancient life on Mars, as they are widely used by terrestrial life as a component to build proteins. Proteins are essential for life because they are used to make enzymes that speed up or regulate chemical reactions, and to make structures.
“Our results suggest that amino acids are being destroyed by cosmic rays in the surface rocks and regolith of Mars much faster than previously thought,” said Alexander Pavlov of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Current missions with Mars rovers drill to about two inches deep. At those depths, it would only take 20 million years to completely destroy amino acids. The addition of perchlorates and water increases the rate of amino acid destruction even further.” A 20 million year period is a relatively short period of time as scientists are looking for evidence of ancient surface life that would have been present billions of years ago when Mars was more like Earth.
This result suggests a new search strategy for missions limited to sampling at shallow depths. “Missions with shallow core samples should look for recently exposed outcrops, for example recent micro-craters less than 10 million years old or the material ejected from such craters,” said Pavlov, lead author of a paper on this study published on 24 October. June was published in Astrobiology†
Cosmic rays are high-energy particles (usually protons and helium ions) generated by powerful events on the Sun and in deep space, such as solar flares and exploding stars. They can degrade or destroy organic molecules when they penetrate yards (meters) into a solid rock, ionizing and destroying everything in their path.
Earth’s thick atmosphere and global magnetic field protect its surface from most cosmic rays† In his youth, Mars also had these characteristics, but lost this protection as he got older. However, there is evidence that billions of years ago the thicker atmosphere allowed liquid water to subsist on the surface of the Red Planet. Because liquid water is essential for life, scientists want to know if life originated on Mars, and look for evidence of ancient Martian life by examining Martian rocks for organic molecules such as amino acids.
The team mixed different types of amino acids in silica, hydrated silica or silica and perchlorate to simulate the conditions in Martian soil and sealed the samples in test tubes under vacuum conditions to simulate the thin Martian air. Some samples were kept at room temperature, about the warmest ever on the Martian surface, while others were cooled to a more typical minus 67 degrees Fahrenheit (minus 55 degrees Celsius). The monsters are blasted with different levels of gamma rays– a type of highly energetic light – to simulate doses of cosmic rays to those received after about 80 million years of exposure to the surface rocks of Mars.
The experiment is the first to mix amino acids with simulated Martian soil. Previous experiments tested gamma rays on pure amino acid samples, but it is highly unlikely that a large cluster of a single amino acid will be found in a billion-year-old rock.
“Our work is the first comprehensive study examining the destruction (radiolysis) of a wide range of amino acids under a variety of Mars-relevant factors (temperature, water content, perchlorate abundance) and comparing the rates of radiolysis,” Pavlov said. . “It appears that the addition of silicates and especially silicates with perchlorates greatly increases the destruction rate of amino acids.”
Although no amino acids have yet been found on Mars, they have been discovered in meteorites, including one from Mars. “We identified several straight-chain amino acids in the Astrobiology Analytical Lab at Goddard in the Antarctic Mars meteorite RBT 04262 that we believe to have originated on Mars (no contamination from terrestrial biology), although the mechanism of formation of these amino acids in RBT 04262 remains unclear,” said Danny Glavin, a co-author of the paper at NASA Goddard. “Since Mars meteorites are typically ejected from depths of at least 3.3 feet (one meter) or more, it is possible that the amino acids in RBT 04262 were protected from cosmic rays.”
Organic matter has been found on Mars by NASA’s Curiosity and Perseverance rovers; however, it is not a conclusive sign of life, as it may have originated from non-biological chemistry. The results of the experiment also imply that it is likely that the organic material observed by these rovers has been altered by radiation over time and therefore not as it was when it was formed.
Alexander A. Pavlov et al, Rapid radiolytic degradation of amino acids in the shallow subsurface of Mars: implications for the search for extinct life, Astrobiology (2022). DOI: 10.1089/ast.2021.0166
NASA’s Goddard Space Flight Center
Quote: NASA experiment suggests we need to dig deep for evidence of life on Mars (June 2022, June 27) retrieved June 28, 2022 from https://phys.org/news/2022-06-nasa-deep-evidence-life- mars.html
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