NASA has spotted a funny chemical signature on Mars, and one of three explanations the researchers have suggested involves the presence of past life.
In recent months, the star of space news was undoubtedly the shock duo made up of Perseverance and its sidekick Ingenuity. One could almost forget that the eldest of the first, Curiosity, still and always surveys the red planet alone; it is recalled today to our good memory with a striking discovery, one of the three potential explanations of which is the presence of past life on Mars.
Like Perseverance, Curiosity is also equipped with a drill that allows it to recover rock samples. It was while analyzing one of these samples collected over the past three years that NASA teams made a very intriguing discovery: they spotted a particular carbon signature which, on Earth, is a marker of biological processes and therefore of life.
Like all rock samples, this one was heated to around 850°C in the bowels of the rover before being passed through the spectrometer. The latter was able to precisely analyze the different carbon isotopes released during the process. In essence, these isotopes represent different “versions” of the same carbon atom, with a difference in the number of neutrons and the mass.
A characteristic marker of terrestrial life
This isotopic analysis is a superb tool. Indeed, if we know which isotope of carbon we are dealing with, it is then possible to formulate hypotheses on its history. For example, we know that on Earth, living beings use an isotope called Carbon 12 as opposed to the heavier Carbon 13. By analyzing the C12 / C13 ratio, researchers have already succeeded in making important discoveries on the biological history of certain terrestrial regions; this is a crucial clue to who lived where, and when.
NASA troops therefore probably frowned when they laid eyes on the results transmitted by Curiosity. Indeed, the rock in question contained a surprisingly high amount of carbon 12 compared to measurements previously carried out on meteorites! Carbon is the basic unit on which life as we know it is built. It is found in soils, in the atmosphere, in water, and in all living organisms known to date.
For researchers, therefore, there is much to be excited about. Because if we were on our good old blue planet, it would indeed be an indisputable sign of life. “On Earth, the processes that produce this type of carbon signature are all biological.”, says Dr. Christopher House. Moreover, at present, there is no element to exclude the possibility that it is a trace of past life.
“Disregard the Earth”
Can we finally say that these researchers have found life on Mars? Absolutely not. For if these data are compatible with this explanation in the terrestrial context, there is nothing to confirm that this is also the case on Mars. “The most difficult thing is to ignore the Earth and our human biases”, explains renowned astrobiologist Jennifer L. Eigenbrode. “We really need to look at the fundamentals of chemical, physical and environmental processes on Mars”, she insists.
In this case, the carbon-12 unearthed by Curiosity could very well have been produced by a different process; there is nothing to confirm that there is a link with a biological activity. The researchers propose two such hypotheses. The first suggests that UV radiation could have interacted with CO2 in the Martian atmosphere, thus producing new carbonaceous molecules. According to the other hypothesis, it could also be a extremely old residue, deposited following the passage of the solar system in a giant carbon cloud.
At present, it is simply impossible to separate things. “LThe data are compatible with the three hypotheses”, explains House. NASA will therefore have to collect more data to answer this question.
Martian geology, the missing piece of the puzzle
In this context, the priority will above all be to focus on the geological cycles of Mars. Its carbon cycle, in particular, is a crucial piece that still eludes researchers. Because on Earth, the latter is today relatively well defined and understood. We already know the majority of the actors involved, and above all the place of life in this carbon cycle. On the other hand, the situation is very different on Mars. Today, researchers’ knowledge of the Martian version of this cycle is still very limited. It is therefore very difficult, if not impossible, to know how life could fit into it.
The researchers will therefore continue to measure the ratio of carbon isotopes at different points of interest; with a bit of luck, they will succeed in observing the same phenomenon again. But above all, they hope to fall on one of these mysterious methane plume, as had already been the case in 2019; the objective would be to carry out a new isotopic analysis on this omnipresent element in the biological cycles of the Earth.
Unfortunately, this event was as sudden as it was unexpected and Curiosity was therefore unable to capture a sample. On the other hand, NASA will now be ready to jump at the chance if it arises again. We still don’t know if Mars once hosted life, but what is certain is that the answer is getting closer!