During the search, the rover probe was equipped with SHERLOC, a tool capable of finding organic molecules. However, we must differentiate between an “organic molecule” and a “organic bio-signature” or a “biomarker”. Organic molecules can be a sign of life, but beware: in fact, few are. We call them biomarkers.
To understand this, let’s think about oil. In the 1930s, the biological origin of petroleum was discussed, until the chemist Alfred Tripps discovered the presence of porphyrins in fossil fuels. It is derived from chlorophyll and cannot be explained by its lifeless existence. So, by studying biomarkers, we know that oil is what remains of ecosystems that evolved millions of years ago.
If SHERLOC finds organic molecules, it must be evaluated if they are valid biomarkers. The problem is that this means that Earth’s metabolism is global. For example, if there had never been photosynthesis with chlorophyll on Mars, we would never find Treibs porphyrin as a biomarker.
Minerals can also be biological signatures:
We collected crystals of formate, an organic compound, in a salt lake similar to the one that might have been present on Mars. The (unlikely) discovery of these crystals on Mars will have a huge impact and the idea of life’s existence will spread on social media.
Unlike porphyrins, formate can be non-biotic (i.e. non-living). It is not a biological marker. We know that the true biological signature is a chemical imbalance with the other components of the lake. The study of biocompanies is difficult and will require transporting samples to the ground.
What if we did not find any evidence of life?
If perseverance finds no sign of life, the task may be viewed by the audience as a failure. Nevertheless, Mars exploration is always successful, both for the knowledge it brings us and for the technologies it produces. Having a planet in which conditions allowed (we think) life to emerge, but initially ceased, would be a unique scenario for understanding the origin of terrestrial life.
It is not a far fetched idea. The Curiosity spacecraft has found materials that could be the key to the origin of life, forming a scenario untouched for millions of years, and devoid of changes caused by a possible biosphere on Mars.
It is possible that no evidence of life on Mars will ever be found, and the question will remain unanswered (no evidence is not evidence of absence). But, if we start from the idea that life never spread on Mars, we can focus on the conditions that we think existed at its origin. If we find the matches, then why hasn’t life ever evolved? Was a component missing? Didn’t the Martian dynamics allow for that? Has another kind of life spread? Through laboratory work and what we know about our planet, we may be able to understand how life began and how it evolved.
If advanced life ever existed on Mars (and bacterial ecosystems exist), questions about the origin of life would remain open. Nevertheless, the lifeless planet Mars could be an opportunity to learn more about our origin.