Mars rock samples are capable of "fooling" the search for life on Mars: they can show non-organic structures entirely similar to biological ones.
Perseverance is collecting its first Martian rock samples, which will arrive on Earth to be finally analyzed only in the next decade. And in 2022 will follow the ExoMars mission, by ESA and Roscomos, which will send another rover - Rosalind Franklin - on the red planet in search of biological traces.
After the alarm for the risk of contamination launched in recent days by researchers at McGill University, today comes a new warning for astrobiologists who will be entrusted with the task of looking for traces of life on Mars.
False traces of life on Mars
The new study, published in the Journal of the Geological Society, bears the eloquent title "False traces of life on Mars: anticipating ambiguity" and is signed by two researchers from the University of Edinburgh, Sean McMahon and Julie Cosmidis.
In the research they summarize the various known chemical and physical processes capable of generating compounds consistent with the existence of life, and trace the stages in which they could have manifested on the surface of the red planet.
The ambiguities that the scholars intend to anticipate concern the next missions devoted to the search for life on Mars: as stated in the study "it is known that the search for life on Mars can produce false positives, in particular through the detection of objects, patterns and substances that may appear to be products of a life form but are not at all biogenic".
The risk that the next important missions may incur in serious errors of assessment must be absolutely mitigated, write the two scientists. So in the research they review all the known processes that could have generated deposits of apparently organic materials in Martian rocks: dozens of processes, only among those known, capable of producing structures quite similar to those visible under the microscope for the most basic forms of life.
A warning for future studies
These processes may have resulted, over the years, in molecular formations and patterns that can "fool" astrobiologists: "we've been fooled by processes that mimic life forms before," says Dr. Cosmidis, so the risk of it happening again is real.
Several times it has happened that non-biological traces have been mistaken for fossilized microbes, both on Earth's rocks and on meteorites from Mars: the similarity of structures can be profound enough to fool even the most experienced eye.
"Our study is a warning to those who will investigate life-mimicking processes on Mars, so that they may not fall into the same traps as in the past again," and mistake phenomena completely unrelated to life for traces of organic or biogenic substances.
Some non-organic processes in fact show signs quite similar to those found in living organisms, and on Mars there are several that can generate ambiguities of this type.
For this reason, the researchers argue, "the origins of any Martian rock specimen that resembles a fossil will certainly be very ambiguous." Sooner or later, a Martian rover will bring rock samples back to Earth that show "signs of life" - at which time we should be able to "accurately distinguish any fossils from these structures" that look organic but have nothing to do with life.
On Mars, in particular, we need to pay attention not only because that's where we're most intensely looking for biological traces, but also because on the planet "for every kind of fossil there's at least one non-biological process that creates things that look very similar" but aren't biological traces at all.