The researchers reported that the salt water just below the surface of Mars could contain enough oxygen to support the kind of microbial life that emerged and flourished on Earth billions of years ago.
As reported in the journal Nature Geosciences on Monday, in some places, the amount of oxygen available could even keep alive a primitive multicellular animal, such as a sponge.
"We discovered that brines," water with high salt concentrations, "on Mars can contain enough oxygen for microbes to breathe," said lead author Vlada Stamenkovic, a theoretical physicist at the Jet Propulsion Laboratory in California, United States.
"This completely revolutionizes our understanding of life potential on Mars, today and in the past," he told the AFP news agency.
Until now, it had been assumed that the minimum amounts of oxygen on Mars were insufficient to sustain even microbial life.
OBSERVATION: Scientists launch the BepiColombo spacecraft to explore Mercury (2:17)
"We never thought that oxygen could play a role in life on Mars because of its rarity in the atmosphere, about 0.14 percent," Stamenkovic said.
By comparison, life-giving gas constitutes 21 percent of the air we breathe.
On Earth, aerobics, that is, breathing with oxygen, life forms evolved along with photosynthesis, which converts CO2 into O2. Gas played a critical role in the emergence of a complex life, notable after the so-called Great Oxygenation Event about 2.35 billion years ago.
But our planet also harbors microbes, at the bottom of the ocean, in boiling hot springs, which subsist in oxygen-deprived environments.
"That's why, every time we think about life on Mars, we study the potential of anaerobic life," Stamenkovic.
Life on Mars?
The new study began with the discovery of NASA's Curiosity Mars rover of manganese oxides, which are chemical compounds that can only be produced with a large amount of oxygen.
Curiosity, along with Mars orbiters, also established the presence of brine deposits, with notable variations in the elements they contained.
A high salt content allows water to remain liquid, a necessary condition for oxygen to dissolve, at much lower temperatures, which makes brines a happy place for microbes.
Depending on the region, the season and the time of day, temperatures on the Red Planet can vary between minus 195 and 20 degrees Celsius.
The researchers devised a first model to describe how oxygen dissolves in salt water at subzero temperatures.
A second model estimated climate changes on Mars over the past 20 million years and over the next 10 million years.
Taken together, the calculations showed which regions of the Red Planet are most likely to produce brine-based oxygen, data that could help determine the location of future probes.
"Oxygen concentrations [on Mars] ", the study concluded, are orders of magnitude" – several hundred times – "more than what aerobic or oxygen-breathing microbes need."
"Our results do not imply that there is life on Mars," Stamenkovic warned. "But they show that Martian habitability is affected by the dissolved oxygen potential."