On February 18, 2021 he landed in the crater Jezero from mars the rover Perseverance, which will study the composition of rocks, the subsoil and the climate. This was the first success of the Mars 2020 mission and its development had English participation: MEDA is an environmental station developed by the Center for Astrobiology (CSIC-INTA).
The arrival of Perseverance has fueled the debate about whether there is or was life on Mars, and its present or past habitability. ‘Habitability’ does not mean that humans can build a house there, but rather defines the geochemical and environmental conditions favorable for the origin and evolution of life. Among the mission’s objectives is to study habitability and search for evidence of ancient microbial life.
Today, as far as we know, it is unlikely that there is life on Mars. Consider that of our planet: for most of its history, the Earth was inhabited only by microorganisms. Evolution took about 3.4 billion years for plants and animals to emerge. It makes sense to assume that, had life existed on Mars, this was microbial.
In space exploration, we take current terrestrial life as a reference, since we do not know another. The downside is that, if evidence of Martian life is not seen (which is likely), we will wonder if it is because we do not know what to look for exactly.
What evidences of life are we looking for?
The Perseverance’s location is no accident. If we want to look for evidence of life, we must go to a favorable place. In the crater Jezero that place could have been: the delta at the mouth of a river. But, the fact that there is evidence that the water formed familiar landscapes, with its rivers and valleys, does not imply that there was life. You have to look for the evidence.
For the search, the Perseverance It is equipped with SHERLOC, an instrument capable of finding organic molecules. However, we must differentiate between “organic molecule” and “organic biosignature” or “biomarker”. Organic molecules could be a sign of life, but be careful: in reality, few are. We call these biomarkers.
To understand it, let’s think about oil. In the 1930s the biological origin of oil was debated, until chemist Alfred Treibs discovered porphyrin in fossil fuels. It is derived from chlorophyll and we cannot explain its presence without life. Thus, studying biomarkers (compounds whose origin we can only attribute to life), we know that oil is what remains of ecosystems from millions of years ago.
If SHERLOC finds organic molecules, it must be evaluated if they are valid biomarkers. The problem is that this implies assuming that the terrestrial metabolism is universal. For example, if there was never photosynthesis with chlorophyll on Mars, we will never find Treibs porphyrin as a biomarker.
Minerals can also be biosignatures:
We collected these crystals of formate, an organic compound, in a saline lake similar to those on Mars. The (unlikely) discovery of these crystals on Mars would have a great impact and the idea that there was life would spread on social networks.
Unlike porphyrin, formate can be abiotic and is not a biomarker. We know it is, because the true biosignature is the chemical imbalance with the other components of the lake. The study of biosignatures is difficult and will require the transport of samples to Earth.
What if no evidence of life is found?
From an advertising and financing point of view, looking for signs of life is a good strategy. It is less media, but that on Mars there is no life, nor has there been, would also be good news.
If Perseverance finds no sign of life, the public could see it as a failure. However, the exploration of Mars is always a success, both because of the knowledge it brings us, and because of the derived technologies. Having a planet in which the conditions that (we think) propitiated life were met, but that this has stopped at the beginning, would be a unique scenario to understand the origin of terrestrial life.
It is not a crazy idea. The rover Curiosity found materials that could be key to the origin of life, forming an intact scene for millions of years, free from the changes caused by a potential Martian biosphere.
It is likely that no evidence of life will be found on Mars, and the question would remain unanswered (absence of evidence is not evidence of absence). But, if we take the idea that life never proliferated on Mars, we could focus on the conditions that, we think, must have occurred for its origin. If what we find fits, why didn’t life evolve? Was there an ingredient missing? Did the dynamics of Mars not allow it? Did a different kind of life proliferate? Together with laboratory work and what we know about our planet, perhaps we could understand how life begins and its evolution.
If advanced life had existed on Mars (and bacterial ecosystems are), questions about the origin of life would remain open. However, a lifeless Mars could be the great opportunity to know our own origin.