Supercool brines on Mars may contain enough oxygen to support aerobic life

Atmospheric oxygen allows complex life and is a characteristic of it. Aerobic respiration is so energy efficient that it would have been necessary for multicellularity. There is virtually no oxygen in the atmosphere surrounding Mars, which raises questions about the prospects for a complex life there.

But it is possible that dissolved oxygen in aqueous brines that might exist on the surface of the red planet or just below. CalTech and Harvard geologists have analyzed exactly how much oxygen these brines could contain and have found that this may be enough.

Some conditions made them think that there was even a chance. First, the Martian atmosphere has a little oxygen, which is very different from what it does not have. ("There is a big difference between most deaths and all deaths.") Secondly, the chemistry of meteorites and Martian rocks indicates that oxygen played a role in the formation of the Martian crust. Third: Brines on the surface of the Martian planet or just below it have a much lower freezing point than pure water because of the magnesium and calcium perchlorate salts they contain. They can cool down to 140-150K while remaining liquid, and colder liquids can dissolve more gas.

Finally, recent experiments have shown that the simplest multicellular life – microorganisms and sponges – requires much less dissolved oxygen for aerobic respiration than most microbials and single animals. So, it would only take a minimum amount of oxygen to support something like these organisms.

The researchers therefore calculated the solubility of molecular oxygen in brines near the Martian surface (since oxygen is in equilibrium with the atmosphere) with different levels of different salts at temperatures between 140 and 300K. They examined brines not only from modern Mars, but also from Mars 20 million years ago, or 10 million years later, noting how conditions would change depending on the weather. axial inclination.

Worst estimates

Even in their most unfavorable estimates, brines could contain twice as much oxygen as the microbes that aerobic respiration needs. At the poles, where it is colder and where brines are more likely to freeze sporadically, they may contain a million times more, enough for multi-cellular sponges to breathe. These oxygen levels are comparable to those observed in the Earth's oceans today and are several orders of magnitude higher than those of the oceans of the early Earth. Comparing these results with different axial shifts over time has shown that Mars has endured much richer oxygen environments over the past five million years.

Here on Earth, photosynthesis probably puts enough oxygen in the atmosphere to open the way to aerobic respiration. But it's not because aerobic life is born here that it's the only way to happen or use that path. Even though there is very little oxygen in the atmosphere of Mars, this work shows that it is possible that there is (or maybe once, maybe one) an aerobic life on March.

Nature Geoscience, 2018. DOI: 10.1038 / s41561-018-0243-0 (About the DOIs).