PARIS - Salty water just below the surface of Mars could hold enough oxygen to support the kind of microbial life that emerged and flourished on Earth billions of years ago, researchers reported Monday (Oct 22).
In some locations, the amount of oxygen available could even keep alive a primitive, multicellular animal such as a sponge, they reported in the journal Nature Geosciences.
"We discovered that brines" - water with high concentrations of salt - "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.
"This fully revolutionises our understanding of the potential for life on Mars, today and in the past," he told AFP.
Up to now, it had been assumed that the trace amounts of oxygen on Mars were insufficient to sustain even microbial life.
"We never thought that oxygen could play a role for life on Mars due to its rarity in the atmosphere, about 0.14 per cent," Stamenkovic said.
By comparison, the life-giving gas makes up 21 per cent of the air we breathe.
On Earth, aerobic - that is, oxygen breathing - life forms evolved together with photosynthesis, which converts CO2 into O2. The gas played a critical role in the emergence of complex life, notable after the so-called Great Oxygenation Event some 2.35 billion years ago.
But our planet also harbours microbes - at the bottom of the ocean, in boiling hot springs - that subsist in environments deprived of oxygen.
"That's why - whenever we thought of life on Mars - we studied the potential for anaerobic life," Stamenkovic.
LIFE ON MARS?
The new study began with the discovery by Nasa's Curiosity Mars rover of manganese oxides, which are chemical compounds that can only be produced with a lot 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 for water to remain liquid - a necessary condition for oxygen to be dissolved - at much lower temperatures, making brines a happy place for microbes.
Depending on the region, season and time of day, temperatures on the Red Planet can vary between minus 195 and 20 deg C.
The researchers devised a first model to describe how oxygen dissolves in salty water at temperatures below freezing.
A second model estimated climate changes on Mars over the last 20 million years, and over the next 10 million years.
Taken together, the calculations showed which regions on the Red Planet are most likely to produce brine-based oxygen, data that could help determine the placement of future probes.
"Oxygen concentrations (on Mars) are orders of magnitude" - several hundred times - "greater than needed by aerobic, or oxygen-breathing - microbes," the study concluded.SUDINI LADIES ITALIAN BLACK LEATHER SHOES NEW SZ 9.5M , Ladies Anne Michelle Silver Diamante Cut Out Detail Flat Shoes F80140 , Vince Navy Blue Coated Woven Canvas Slip On Sneaker Flat Shoe Size 9.5 , ECCO Black Mary Jane Walking Shoes Women's US 6.5 Professional Work shoeVan Eli Women's Brown Shoes 7 M , Adolfo Dominguez Shoes Loafers Women Size 38 US 7 Brown Tan Leather UpperFitflop Womens Rokkit Slide Open Toe Sandal Shoes, Supernavy, US 10 , Bernie Mev Women's Cuddly Mary Jane Flat, Black, 38 EU/7.5-8 M US , Nine West Womens Norella Leather Almond Toe Loafers, Cognac, Size 9.5 MCEC , Jessica Simpson Mandalaye Ballet Flat Coffee Women's Size 7.5M LeatherShoes For Crews Womens Mary Janes Black Leather Rocker Toner Sneakers size 7.5 MWomens Nike Flex Experience Rn 4 Training Grey White Size 10 749177 018 , NIKE Huaraches White Neon Pink Blue Gently Worn Size 7 , K-Swiss Shock Spring Leather Athletic Shies Women's Size 8.5 92648155 , Merrell Hiking Shoe Women’s Waterproof Beige Siren Sport Size 8New Bakance 409 Women's Size 7.5 , Custom? Nike Free Run+ 2 NikeID Bad Kitty Obsidian Blue Wolf Gray Sz 9.5 Womens , Women's New Balance 577 Shoes Sneakers Size 9.5D Wide Running Gray Yellow N5FILA SKELE-TOES Women's Walking / Running / Climbling Shoes EZ Slide Drain Sz 9 , Saucony Ride 8 Women US 9 Wide Blue Silver + Purple Athletic Running ShoesBCBGeneration Womens Cleo Low Top Slip On Fashion SneakersNike Womens Air Max Sequent 3 Gray Running Shoes Size 12.5 (424248)adidas Edge Lux Clima - Black - Womens , Asics Gel-Kayano Trainer Knit Sneakers Shoes H7N6N 8787 Women Size 10 , Womens ADIDAS HARD COURT HI W Black Pink Synthetic Trainers Q21305 , Pre-owned Women Nike air Max Classic Air Force 1 315677 002 Black Size 7.5 , Women's Nike Duel Racer Running Shoes NEW Khaki/Carbon/Sail/Bone, MSRP $120ASICS Women's Gel-Moya Running Shoe Mid Grey/Silver Size 11New Balance Womens Ww928hw2 White Walking Shoes Size 12 (326156) , Asics Gel-Fortrus TR Women's Training Shoe S384Y 9001 Size 11.5
"Our results do not imply that there is life on Mars," Stamenkovic cautioned. "But they show that the Martian habitability is affected by the potential of dissolved oxygen."