Salty, Oxygenated Water on Mars Could Host Simple Aerobic Life

Caltech researcher Vlada Stamenković and co-authors calculated that if liquid water exists on the Red Planet, it could contain more oxygen than previously thought possible.

Stamenković et al find that modern Mars can support liquid environments with dissolved oxygen values ranging from 2.5*10−6 mol /m3 to 2 mol/m3 across the planet, with particularly high concentrations in polar regions because of lower temperatures at higher latitudes promoting oxygen entry into brines. Image credit: NASA / JPL-Caltech.

Stamenković et al find that modern Mars can support liquid environments with dissolved oxygen values ranging from 2.5*10−6 mol /m3 to 2 mol/m3 across the planet, with particularly high concentrations in polar regions because of lower temperatures at higher latitudes promoting oxygen entry into brines. Image credit: NASA / JPL-Caltech.

“Nobody ever thought that the concentrations of dissolved oxygen needed for aerobic respiration could theoretically exist on Mars,” Dr. Stamenković said.

“Oxygen is a key ingredient when determining the habitability of an environment, but it is relatively scarce on Mars,” added Caltech’s Professor Woody Fischer, co-author of the study.

In recent months, data from ESA’s Mars Express orbiter have suggested that liquid water may lie beneath a layer of ice at the planet’s south pole.

It has also been hypothesized that water could exist in salty subsurface pools, because perchlorate salts have been detected at various places on Mars.

Salt lowers the freezing point of water, which means that water with perchlorate in it could potentially stay liquid despite the freezing temperatures on Mars, where summer nights on the equator can still dip down to minus 100 degrees Fahrenheit (minus 73 degrees Celsius). That hypothetical salty water is what interested the study authors.

Oxygen enters water from the atmosphere, diffusing into the liquid to maintain an equilibrium between the water and the air.

If salty water were close enough to the surface of the Martian soil, then it could effectively absorb oxygen from the thin atmosphere.

To find out just how much oxygen could be absorbed, the team developed a chemical model describing how oxygen dissolves in salty water at temperatures below the freezing point of water.

They then examined the Martian global climate and how it has changed over the past 20 million years, during which time the tilt of the axis of the planet shifted, altering regional climates.

The solubility and climate models together allowed the researchers to infer which regions on Mars are most capable of sustaining high oxygen solubilities, both today and in the planet’s geologically recent past.

They found that, at low-enough elevations and at low-enough temperatures, an unexpectedly high amount of oxygen could exist in the water — a value several orders of magnitude above the threshold needed for aerobic respiration in Earth’s oceans today.

Further, the locations of those regions have shifted as the tilt of Mars’ axis has changed over the past 20 million years.

During that time, the highest oxygen solubilities have occurred within the past 5 million years.

“Our results could inform future missions to Mars by providing better targets to rovers searching for signs of past or present habitable environments,” Dr. Stamenković said.

The findings appear online this week in the journal Nature Geoscience.

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Vlada Stamenković et al. O2 solubility in Martian near-surface environments and implications for aerobic life. Nature Geoscience, published online October 22, 2018; doi: 10.1038/s41561-018-0243-0

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