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.Hush Puppies SHOES WOMENS SIZE 7 MNine West women's chunky cork heel BROWN 7.5M fabric platform shoe NICE , WOMEN'S BORN LEATHER CUSHION INSOLE MULES SZ 6 1/2 US 37 EU , Sperry Top Sider Pink Sequence Boat Shoes Womens Size 8 MSkechers BOBS From Women's Pureflex-Supastar Wide Flat Black/Black 7 W US , Wanted "Rosebuds" Slip-On Sneaker with Floral EmbroideryMerrell Womens Size 8 Mary Jane Plaza Bandeau Brown Leather Walking Shoes Mint , Cole Haan Women's Flats Gilmore Ballet Rose Gold Metallic 9.5BMerrell Encore Ice Clogs- Women's Size 10, BrownSam Edelman Talia Slip On - Women's Size 5M BlackNautica Rudder Slip-On Espadrille Flats, Navy Triple Stripe, 8.5 US / 39 EU , Womens Nine West Brown Leather Flats 9.5 M NEW , Nine West Womens Xalan Leather Closed Toe Loafers , J.CREW Women's Black Smooth Leather Mary Jane Shoes Made in Italy sz 8.5 , Sperry Top-Sider Pier Sneaker - Women's Size 4 M, Grey/Silver , Puma Roma womens white sunny lime yellow leather tennis SHOES sneakers size 9NEW WOMEN'S REEBOK TRAVEL TRAINER SLIP-ON SHOES SIZE 7Hush Puppies Cottonwood Men's Slipper size 12 M , Keds Womens Fashion Sneaker Size 11 (16960)Chic Hidden Wedge Heels Rhinestone Mesh High Top Womens Sneakers Athletic ShoesNike Air Shox Zoom Experience Women's US 5 Running Shoes Black Silver 318685-001 , BROOKS DYAD 8 Running Training Shoes Women's Size 8.5 Blue Gray Sneakers , Vintage Reebok suede sneakers NWT size 9 , Nike Air Force 1 Ultraforce Mid Vachetta Tan White 864025-200 Women's Size 6 NEWSTEVEN by Steve Madden Women's Laguna Sneaker Leopard Size 7.5Women's Shoes Ahnu AF2473DGRY Sugarpine Hiking Air Mesh Grey Orange 8M US 39 EU , Puma Barnett Vintage Met Womens Leather Sneakers Shiny Metallic Shoes - GoldNew Balance 859 Sz 7.5 B Women Gray Blue Running Shoes EUC YGI A8 , Skechers Women's "Graceful - Beauteous" Multicolor Running Shoes Size 6 NIB , Skechers Women's Go Step Lite Lux Walking Shoe ,
"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."