On Earth, methane is one of our most potent greenhouse gases; many times more harmful than carbon dioxide and one of the oldest waste products of life on our planet. On Mars, previous evidence has suggested that it once had potentially favorable conditions for the development of life, but we have never established this scenario quantitatively.
However, a new simulation by a team of scientists led by astrobiologist Boris Sauterey of the Institut de Biologie de l’Ecole Normale Supérieure (IBENS) in Paris, France and published in the journal Nature Astronomy , suggests that early Mars likely harbored microorganisms that fed on hydrogen and produced methane, considered to be some of the first forms of life on Earth. Also, on Mars, these methanogenic microbes would have had a very different effect on the Red Planet: They would have caused runaway cooling instead of warming.
An entire ecosystem of hydrogen phagocytes
According to the study, microorganisms that feed on hydrogen and excrete methane could have thrived on Mars about 3.7 billion years ago, around the same time that primitive life took hold in Earth’s primordial oceans. Unlike what happened on Earth, where an environment conducive to more complex life forms was gradually generated, exactly the opposite happened on Mars.
“The crust of Mars may have provided a favorable environment for microbial life. The brine-saturated porous regolith would have created a physical space protected from ultraviolet and cosmic radiation,” the researchers point out, adding that the number of microbes produced on early Mars “could have been as high as in the oceans of early Earth.” ”.
Too cold
Yes indeed. The cooling effect of these microorganisms on the planet would have forced them to move progressively deeper into the Martian crust.
“Spatial projections of our predictions point to lowland sites at low to mid-latitudes as good candidates for discovering traces of this early life at or near the surface,” the researchers wrote.
The researchers built a model of Mars from the Noahic period, a time in Martian history when it was frequently bombarded by asteroids, had a thick atmosphere and likely liquid water on its surface. Could creatures like methanogens, some of the simplest and hardiest creatures known, have thrived there and then?
Simulation results
In the computer simulation they found that as Martian methanogens pumped more methane into the atmosphere, the model planet teemed with life below the surface for a few hundred thousand years. But methane’s interactions with the Martian atmosphere and its briny ice caps caused the planet to cool to the extreme. The melting point of Martian ice plummeted past a point of no return . Within the next half million years, Mars would be almost completely covered by an ice cap, according to model predictions.
And it is that being further from the sun than Earth, Mars needed those greenhouse gases to maintain a comfortable temperature for life. But as those early microorganisms began gobbling up hydrogen and producing methane, they slowed down the warming and led to Mars finally becoming an inhospitable place.
Experts point out that the developed model would be a good tool to help understand if the planets of our solar system and others could harbor life. Instead of early life being easily self-sustaining, biospheres could enter feedback loops that lead to their own deterioration.
What the experts say
“This is research that addresses Martian habitability from a theoretical point of view, making high-quality theoretical models that are really interesting and innovative, although, in my opinion, astrobiologically speculative. Considering an ‘ecological model’ of Mars, when there is still no evidence of life or its potential biomarkers, is an interesting exercise, with valid conclusions regarding what is suggested and the methodology used, but which would require greater solidity and scientific rigor , beyond the purely theoretical. So far there is no evidence of life on Mars or biomarkers of its past or present existence. Although this hypothesis, or others, is not ruled out, there is no evidence of the existence of methanogens either today or in the past. In fact, there is a whole very interesting open debate about the actual existence (or not) of methane. I think this point should have been addressed in more detail, since the existing evidence about methane is still the subject of scientific debate.
In my opinion, the authors have made an excellent theoretical approach, but limited exclusively to what it is: a theoretical model”, Jesús Martínez Frías, planetary geologist and astrobiologist at IGEO (CSIC-UCM), explains to Science Media Center Spain .
“From the missions currently under development on Mars, experimental data is being offered, both from the current geology, from the atmosphere, from the past geological record, from the mineralogy and geochemistry of Mars, including interpretations on paleoenvironments and habitability based on all the parameters indicated above. I believe that it will be these detailed analyzes that will allow us to confirm or not in the future the validity and importance of the proposed model”, concludes the expert.
Referencia: Sauterey, B., Charnay, B., Affholder, A. et al. Early Mars habitability and global cooling by H2-based methanogens. Nat Astron (2022). https://doi.org/10.1038/s41550-022-01786-w
