Oxygen is not enough to talk about habitability on Mars, warns the researcher at the Center for Astrobiology (CAB) Alberto González Fairén, who recalls that there are other factors that do not allow habitability in the red planet: very low temperatures, radiation and high concentrations of salts.
This is how this astrobiologist referred to work published on Monday in the magazine «Nature Geoscience» by NASA scientists, who have developed a model to calculate the amount of oxygen in salty waters located just below the Martian surface.
According to NASA, these salty waters could hold enough molecular oxygen to sustain the life of microbes and sponges.
For Fairén, the starting hypothesis of this work led by Vlada Stamenkovic is correct: when oxygen is available for respiration, living beings increase in size and complexity.
"We know this because the first animals on Earth could have been sponges that lived 650 million years ago," points out Efe the Spanish scientist, who adds that these primitive sponges evolved just as a result of the first significant accumulation of oxygen in the terrestrial atmosphere, generated by photosynthetic bacteria.
According to Fairén, the article includes "an interesting comparison", since the authors choose the group of terrestrial organisms that are capable of living at lower dissolved oxygen concentrations in water, which are basically certain types of bacteria and sponges.
From there, the authors conclude that the calculated oxygen concentrations that may exist in the Martian brines would be enough for these organisms to thrive on Mars today.
"Of course, it's just a graphical comparison to highlight the high levels of dissolved oxygen in these brines: the authors do not imply that sponges can exist in bags of liquid hidden in the ice of Mars."
In addition, underlines the CAB scientist, the work leaves several questions unanswered.
On the one hand, it does not go deeply into the problem of habitability, which is multifactorial, that is, "the possible inhabitants of the brines would not only depend on the oxygen available to breathe".
In this sense, Fairén remembers that there are other factors that do not allow the existence of life similar to the terrestrial one near the surface of Mars today: fundamentally, the lowest temperatures, the highest concentration of salts and radiation.
Therefore, "it is complicated to propose that Martian brines are habitable by life forms similar to terrestrial ones only because they are capable of absorbing a certain concentration of oxygen, without computing the other variables".
The other problem is that, according to Fairén, the presented model does not solve how to explain the very existence of brines that trap oxygen: the authors assume that Mars can hide brines in different places at present and especially at a shallow depth in the polar areas, but "this is a very risky assumption".
Fairén explains that direct observations with «landers» and «rovers» do not support this possibility: although some models seem to predict that, in fact, there may be brines in different places, these same models assure us that they would only be liquid during some hours and at night, when the relative humidity is higher and the temperature reaches values minima.
"There is so little oxygen on Mars that you have to spin very thin to propose works that study the availability of oxygen for living beings," says Fairén, who concludes: the models of the article seem correct, their implications are scarce and irrelevant. EFE