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.WOMENS GIRLS SHOES LADIES PUMPS TRAINERS SLIP ON SPORTS RUNNING CASUAL GYM SIZE , BORN HANDCRAFTED BROWN LEATHER STRAPPY HEELS CLOGS SLIP ONS MULES 40.5 9 MINT!!!City Classified COMFORT SHOES WOMENS SIZE 6 WNINE & CO Women's Shoes Flats Thongs Silver Size 8.5M , Dolce Vita Loafer Flats Size 7.5 Black Leather Reptile Print Comfort Sole , EUC Lands End Wide alpargata Slip On Shoes Size 7 1/2 D MultiMadden Girl Women's Stripess Slip-On Flat,Taupe Fabric,6 M US , Lika Mimika Womens 8 Eur 39 Blue Suede Espadrilles Sneakers Shoes EUCWOMEN'S SAS 'GENUINE HANDSEWN' BLACK OXFORDS 9 MROCKPORT -Women Blue Patent Leather shoes 7 1/2 - 8M , Nine West Women's Shutout Fabric Loafer Flat , LIFE STRIDE Lifestride EVA Womens Brown Shoe Clog Size 8M Low HeelClarks Ladies Evianna Boa Brown Leather Shoes D Fit (R3B) , G by Guess Olisa High Top Fashion Sneakers 305, Medium Blue, 6.5 USStuart Weitzman Metallic Leather Loafers Womens Size 6.5 Stretch MoccasinsWomen's Croc Cobbler Split Suede Clogs Mules Faux Fur Slip-on Shoe Tan Size 9 , RocSoc Women's 8699 Water Shoe , Teva Women's "Sheeba" Rust & Black Suede Clogs Mules Sz 8 Zipper Athleisure , Womens Reebok CrossFit Nano 7 Weave Electric Flash Training SIZE 6.5 , BALLY GOLF Eagle Leather GOLF Shoes Womens US 8.5 Euro 39.5 NWT , NEW BALANCE Womens WL520MR Classics Shoe US 7.5 BLACK/GOLD NEW , EUC Nike Zoom PEGASUS 31 Hyper Pink Running Shoes 654486-600 SZ US 10 WOMEN'S A6 , Womens Merrell Versatrail Trail Running Shoes Size 7 Beet Red Coral Tan J310563C , Columbia techlite waterproof SNEAKER hiking boots shoes SZ 10 MNew Women's Skechers 11930 D'Lites Biggest Fan Athletic Shoes Size 6 (N14)PUMA Women's Cell Riaz Sneaker - Gray New! , CESARE PACIOTTI shoes sz.6.5 (37) silver canvas S5147Brooks Ariel 16 Running Shoes Sneakers Womens Size 7 Aqua Blue/Black-Extra WideSkechers Womens Enough Said Sneaker Shoe, Taupe, US 10New Womens Girls Sport Platform Wedge Air Max Trainers Shoes Sweet Sneaker Boots
"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."