Mars Rovers Have To Dig 6.6 Feet For Signs Of Past Life: Study

Finding signs of past life on Mars may require a little more digging. In a NASA experiment, scientists found that rovers would actually have to dig 6.6 feet to find evidence.

Amino acids are "fundamental to life as we know it," and thus are "reasonable" targets in the search for evidence of life on Mars, the researchers wrote in their paper published in Astrobiology.

But finding such samples could be a little bit tricky. Amino acids and other organic molecules close to the surface can degrade when they are exposed to cosmic rays, which NASA explained to be the particles that are generated from powerful events on the Sun. They can destroy organic molecules when they penetrate solid rock.

Although the Earth is protected from cosmic rays, thanks to our magnetic field and atmosphere, the same cannot be said for Mars, which is believed to have lost these features with age. But through missions such as that of the Perseverance rover, scientists aim to find evidence of past life by searching for molecules such as amino acids.

For their work, the researchers mixed amino acids in silica, hydrated silica or silica and perchlorate to simulate Martian conditions and placed them in test tubes under vacuum conditions that simulate Martian air, NASA noted. They kept the samples at different temperatures, then exposed them to gamma radiation at varying doses.

"We found that irradiation of amino acids mixed with dry silica powder increased the rate of amino acid radiolysis, with the radiolysis constants of amino acids in silicate mixtures at least a factor of 10 larger compared with the radiolysis constants of amino acids alone," the authors wrote. "The addition of perchlorate salts to the silicate samples or hydration of silicate samples further accelerated the rate of amino acid destruction during irradiation and increased the radiolysis constants by a factor of ~1.5."

"It turns out that the addition of silicates and particularly silicates with perchlorates greatly increases the destruction rates of amino acid," the study's lead author, Alexander Pavlov of NASA's Goddard Space Flight Center, said in the NASA feature.

This suggests that amino acids can actually be destroyed by cosmic rays faster than previously thought, Pavlov explained, before adding, "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."

It's worth noting that the evidence of life scientists are looking for dates back to billions of years when Mars would have been a bit more Earth-like, according to NASA. As such, 20 million years is considered to be a relatively short time.

Based on these results, then rovers would have to dig some 6.6 feet or about two meters from the surface to get the evidence they need. This, according to the researchers, poses a "serious challenge" for the mission to find biosignatures on the top two meters of the Martian surface.

This is why, for missions where the sampling is "limited" to shallow depths, it would be best to target "recently exposed outcrops," perhaps "microcraters" that are less than 10 million years old, Pavlov noted.