Get your diggers ready.
A new NASA laboratory experiment shows that rovers may have to dig roughly 6.6 feet (two meters) or more under the surface of Mars to find signs of ancient life due to the effects of ionizing radiation on small molecules such as amino acids.
The discovery of certain amino acids on Mars would be a strong indicator that life once existed on the red planet due to the fact they are used by terrestrial life as a component for building proteins.
The issue is that these are obliterated by cosmic rays, meaning many remnants of ancient Martian life may now be long gone.
Destructive cosmic rays may slow the search for ancient Martian life
In a new study, published in the journal Astrobiology, NASA researchers showed that amino acids are destroyed by cosmic radiation much faster than previously believed.
“Our results suggest that amino acids are destroyed by cosmic rays in the Martian surface rocks and regolith at much faster rates than previously thought,” said Alexander Pavlov of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Current Mars rover missions drill down to about two inches (around five centimeters). At those depths, it would take only 20 million years to destroy amino acids completely. The addition of perchlorates and water increases the rate of amino acid destruction even further.”
The word ‘only’ followed by 20 million years might seem a little strange, but we’re talking in massive timescales due to the fact that life would have likely existed on Mars billions of years ago when Mars was more Earth-like and had lakes and flowing rivers on its surface.
The research suggests that missions that can only drill to shallow depths, including NASA’s Perseverance and Curiosity rovers, should change their sampling strategies based on the new findings. “Missions with shallow drill sampling have to seek recently exposed outcrops – e.g., recent microcraters with ages less than 10 million years or the material ejected from such craters,” said Pavlov, lead author on the new study.
Simulating conditions on Mars
For their research, the team mixed several types of amino acids in silica, hydrated silica, or silica and perchlorate to simulate the conditions on Mars. They then sealed the samples in test tubes under vacuum conditions to simulate the thin Martian air.
These samples were blasted with different levels of gamma radiation to simulate the cosmic rays penetrating the Martian surface in real life — they applied enough radiation to account for up 80 million years of exposure on the red planet. The researchers also applied different temperatures, going as low as minus 67 degrees Fahrenheit (minus 55 degrees Celsius).
“Our work is the first comprehensive study where the destruction (radiolysis) of a broad range of amino acids was studied under a variety of Mars-relevant factors (temperature, water content, perchlorate abundance) and the rates of radiolysis were compared,” Pavlov explained. “It turns out that the addition of silicates and particularly silicates with perchlorates greatly increases the destruction rates of amino acids.”
NASA’s Curiosity rover recently analyzed the amount of organic carbon — a key ingredient for life — found in Martian samples, showing that there were similar levels to some parts of Earth. Curiosity and Perseverance will continue to investigate the red planet’s surface, though they may soon alter their strategies to look for more recently unearthed samples.