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.NEW Black faux leather SLIP ON MOCCASIN LOAFER mini wedge JOB WORK Shoes sz 10 , KIM ROGERS "VALERA" Brown Leather & Satin Upper Kitten Mules in Box Size 8.5Earth Shoe Michelle Shoes, Women's Size 6.5 US, BlackWomen's SAS Simplify Loafers Shoes Size 12S Black Leather Horsebit Tripad AC15Yellow Fabric/Blue Polka-Dots TORY BURCH Ballet Flats 8 MLFL by Lust for Life Women's Tinker Ballet Flat, Blue, 6 M USWhite Mountain MOONDANCE W14895SM Womens Moondance Ballet FlatPAUL GREEN Munchen Gray Metallic Leather Deco Zipper Flats Women's Shoe Size 9 , Ecco Ladies Taisha Blue Misty Modern Ballerina Flat Shoe US 10-10.5New Balance 680 v2 Running Shoes Blue W680BB2 women's size 9.5 , Womens Running Sports Shoes Leisure Sneakers Breathable Athletic Outdoor TrainerWomen's New Balance 520 v1 Sneakers Blue 6.5M , Howsty x Anthropologie Womens Taizz Espadrilles Shoes Black White Size 39 NewNike Air Gray Purple Peach Running Shoes Sneakers Women's Size 8FILA Womens Running Shoes Pink Gray Sneakers Size 7 MROCK-N-FIT NEW WALKING TONING HEALTH FITNESS SHOES WOMENS SIZE 6 WHITE PURPLE , NEW BALANCE 574 WOMEN'S NAVY CLASSIC SNEAKERS 1440 SIZE 8.5 US B W574SMP , The North Face Womens Sz 6 Gore-Tex Vibram Brown Pink Trail Hiking Outdoor ShoesPaperPlanes Women Summer Slip On Sneakers Mesh Flat Shoes Loafer SN502 CAWomens PATAGONIA Amaranth/Turmeric Gray & Purple Running Walking Shoes SIZE 7 , Brinley Co Womens Glitter Faux Leather Slide Sneakers Slip On New , Women's 574 CNA NOIR BLANC JAUNE Superior In Quality Athletic ShoesNew Balance Women's WW577VNew Balance W990NV3 Women's Everyday Running Shoes, Navy , 2013 Womens Nike Free 3.0 V5 EXT Wolf Grey/Red Violet/Anthracite Shoes! Size 9 , NEW Nike Wmns Rosherun Print 599432-137 Womens Shoes Trainers Sneakers SALEVANS Court Mid DX (Leather) Drizzle Grey Skate Shoes UltraCush WOMEN'S 8 , BROOKS RAVENNA 6 WOMENS RUNNING SHOES - DRESSBLUE - LAGOON - SHARPGREEN - SIZ- 6New Women's Skechers12087 Encore- Be Seen Sport Training Shoes Size 7.5 (N19) , Womens Adidas Stan Smith Trainers Sneakers Multicolor Shoes Canvas Flowers sz 10
"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."