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The search for liquid water on Mars in 2015 has reinforced the hope that signs of life are hiding somewhere on the red planet. But in practice, scientists have more or less ignored whether these specific bodies of water had anything to do with life today. The only way that water could exist in liquid form on such a cold planet, is if it was saturated with salt, which lowered the temperatures below the freezing point. Briny water is not considered the ideal place for life, so it springs and evolves.
But all this water may deserve another look. New discoveries published in Nature Geoscience Monday suggest that these pools might contain more breathable oxygen than we had imagined – enough for life to exist on or near the surface .
This opens up some new possibilities for life on Mars, especially those that were not possible on the early Earth, "says Lewis Ward, a Harvard University geobiologist and co-author of the new study.
It is believed that the Martian atmosphere contains only 0.145% oxygen, while about 21% swirls across the Earth. This number does not necessarily kill the dreams of Martians; After all, the first forms of life on Earth did not have access to free oxygen for the first billion years (the evolution of photosynthesis solved this for us). But because oxygen allows the body to use a lot more energy, a lack of oxygen freezes any hope of finding a life at least a few notches above its basic level.
However, good conditions could allow large amounts of life. Oxygen dissolves in these Martian reserves, especially since oxygen dissolves better in the water at lower temperatures. Unfortunately, "no one previously had really thought about the amount of oxygen that may be present in liquid water on Mars because we had no evidence that oxygen had been present. really played a big role, "says Ward. "It is the first attempt to really understand how much oxygen there could be today."
The investigation is based on the presence of manganese oxide on the Martian surface. On Earth, traces of oxides of manganese oxides occurred at about the onset of oxygen accumulation in the atmosphere, about 2.5 billion years ago. Unlike iron (which is responsible for the reddish appearance of the red planet), manganese is quite difficult to oxidize, and the only way to detect oxidation on Earth is either very slowly or is with the help of biology.
But in 2014, the Curiosity rover discovered very concentrated manganese deposits on Mars, which prompted Ward and his colleagues to wonder if they contained close to the aqueous environments containing the necessary oxygen to oxidation. Oxidation of manganese is quite closely (though certainly not exclusively) related to biological activity. The study could be thought of as a matryoshka doll made up of questions: first, how much oxygen do you need to oxidize manganese? So, is this concentration of oxygen able to exist in Martian waters? And finally, at the heart of the study: does this amount of oxygen increase the possibility that oxygen-breathing organisms exist on Mars?
"If there is enough oxygen to do chemically useful work by oxidizing manganese, it suggests that there is enough to do biologically meaningful work too," says Ward
The new study provides encouraging answers to these questions, and the team has developed models for six different salt concentrations, capable of maintaining liquid temperatures from -207 degrees to about 80 degrees Fahrenheit, and The models say that all this salty liquid is more than capable of capturing the pitiful amounts of oxygen dispersed over the Martian surface. there was more oxygen on Mars than on Earth at the beginning of photosynthesis, Ward explains. "This suggests that there may be enough [oxygen] for you to use it. to stimulate the m Ethanol microorganisms. "For aerobes that use oxygen to consume carbon," it turns out that these brines actually contain a lot of oxygen to support the bacteria and the results suggest Also, there is enough oxygen on the surface and below the surface of Mars to allow the recovery of energy from other sources, such as methane and iron.
Sponges are a particularly useful model for thinking about what might survive. these environments. "Sponges are one of the first species of animals to evolve," Ward says. They are simple filter filters that can survive on bacteria and survive in very simple ecosystems. Ward admits that "to be able to examine the potential of life on Mars and other planets, we'd better think exclusively in terms of microbes," but it's interesting to think of the attenuated oxygen requirements of sponges when we let's think about what we could do. evolve on Mars.
Ward and his team hope that the results of this study will be a first step in helping scientists to map areas of the planet Mars that can withstand the highest oxygen concentrations, based on temperature and pressure atmospheric, and superimpose them on another map. illustrates the main hydrogen and methane points on the planet that can be consumed in energy. "We could actually point to places on Mars that have the greatest potential for detection of biological activity" and potential biombad, he said. The study could also help us better understand the potential that other worlds like Europa might have for promoting life.
Of course, there are reasons to be a bit cautious about the implications of the study, which is based on computer modeling and not on direct observations. It will be difficult to confirm the results – not only on Mars, but also on Earth, where scientists have not yet been able to conduct controlled laboratory experiments that correctly measure the solubility of oxygen in very cold brines . On Mars, we must be able to study brines sufficiently in contact with the atmosphere to facilitate gas exchange and allow oxygen to dissolve in the air.
Jonathan Toner, an astrobiologist at the University of Washington, did not participate in the study, said the paper did a good job in showing that the oxygen content of Martian brines was not a limiting factor for life, and that it was also interesting to see a discussion about the interactions of the atmosphere with brines, which "could also have implications beyond habitability," he says. It nevertheless emphasizes that a high rate of oxygen is only possible here with extremely high salinity levels, which is "very difficult" for life. Combined with average temperatures as low as -67 degrees Fahrenheit, "and you have conditions that are not known to support life on Earth. Life does not require that a factor, for example an oxygen supply, but a whole range of factors present at the same time. "If life exists on Mars today," it should adapt to extremely low nutrient reserves at low temperatures and it is known that high salinity, tolerated to an extent bigger than anything the Earth lives on. "
Yet few studies have suggested so far that we could dare to dream of such complex life forms on Mars. But every year, Mars proves more tempting than expected. Scientists charged with searching for life on the red planet have a lot to check on their to-do lists.
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