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.SC35 Nixine Slip On Flats 706, Black, 6 USWomen's Size 10 Flats Shoes Floral Pink Bows (S24)EUC! BORN WOMENS LEATHER BROWN SLIP ON CLOGS SHOES SIZE 8 M 39MERRELL Women's 7 CIRCUIT MJ Brown Mary Jane Suede Ortholite Air Cushion Shoe , Diane Von Furstenberg Womens Black Gold Jeweled Ballerina Ballet Flats SZ 6.5 MTEVA ~ Burgundy Nubuck Suede Leather Comfy Loafers Sz 7 S/N * VG- EXCELLENTWomens 7.5 M Me Too Janell Red Ballet Flats Shoes Slip-On Loafers Wedge Comfort , Annie Shoes Women's Eagle W Ballet Flat, Peach, 8 W US , **Rockport Raelyn Knit Ballet Flats, Women's Size 5.5M, Teal/GreyCity Shoes Valent Strut28 Womens Black Gold Synthetic Trainers , Comfortiva Womens Renee Leather Closed Toe Ballet Flats , Nine West Womens Akeelah Suede Pointed Toe Loafers, Green, Size 6.0 , COLE HAAN G Series Women Casual Slip On Shoes Size 8.5 Brown LeatherSaucony - G Varana Vizi Coral Blue : SC50275 size 11.5 (342) , Fly Flot Men's Slipper, Felt Fabric, Black, Footbed NEWMens Genuine Sheepskin Slippers Moccasins Mules Boots Warm Fur Wool , WOMANS ROCKPORT WALKING CASUAL SNEAKER APW31907 SIZE 8 N WHITEGlaze Women\'s Low Top Strap Fashion Sneaker - Slip On Casual Shoes, Taupe, SizeWomen's Bobs Skechers Pureflex 2-Knockoutz Black 31401/BLK With Memory FoamPUMA Osu NM Sneaker - Women's Size 7.5, Black/RedMIA High-top Quilted Blue Gray & Pink Trainers Sneakers Sz 6, 6.5, 7, 7.5 NWOB , Puma CLYDE GCC - Black - Womens , NEW SCHOLL ORTHAHEEL VENUS WOMENS COMFORT SUPPORTIVE ACTIVE CASUAL SHOESVANS SK8 Hi Slim Zip (Leather) Zephyr Blue/Blanc de Blanc WOMEN'S Size 8.5 , New Balance Women WL574ER Classic Sneakers, Burgundy/ White , CONVERSE CT LEAGUE HI SA Unisex Trainers 149326CNike 904651 100 Free TR 7 Running Shoes-Women's size 11.5 White , Skechers Shape Up Gray Pink Toning Walking Shoes Women's US 8.5M (SK1)Adidas Womens Aw4409 White/Black/White Tennis Shoes Size 8.5 (360181) , Converse Chuck Taylor All Star Lo Top Black Womens 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."