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.Women’s Shoes DexFlex Comfort 2” Wedge Heel Slip-on Black/Gray/Red size 7.5 , LUCKY BRAND leopard-print distressed leather stretchy ballet flats, size 9M , � City Sneaks Canvas Sneakers Women's size 9.5 M Lavender & Teal Floral PrintAMBERY-2-42 WOMEN POINTY-TOE EMBROIDERED MULE ELEGANT REDI LOVE COMFORT Womens Flats Shoes Size 10 M / 42.5 Brown Leather Basket Weave , Ahnu US 8.5 black leather Mary Janes loafers flats shoesGEOX Respira Boots Velours et Synthétique T 37 ETAT NEUF , Naturalizer Shoes Gloria Slip-On Loafers - Women's Size 5.5M - Brown , Cole Haan Womens GR046 Closed Toe Ballet Flats Peony Size 6.0Jack Rogers Zooey Ballet Flats Round Toe Fabric Chain Link Midnight Blue 5.5 MCorso Como Tuxe Ankle Strap Ballet Flats 504, Black, 7.5 USGotta Flurt By Merit Destiny Silver Womens Shoes Athletic 6.5MWOMEN'S ADIDAS TRAIL RUNNING SHOES SZ 7.5 39.5 B USED 990753 SNEAKERS HIKING , Riot by Rampage Women's Daria1 Fashion Ankle Sneaker Shoes Denim Pink Size 6 M , Girls Womens Round Toe Sequins Mesh Hidden Heels Breathable Casual Sneakers G , NICE Reebok Women's NFL Green Bay Packers Sneakers Pink/gray Running Shoes-6.5 , Nike Court Tradition 2 315161-111 White Silver Swoosh Women's US Sz 11 UK Sz 8.5 , Nine West Sophie Slip-On Fashion Sneakers, Black MultiAltra The One 2.0 Relaxed Running Training Purple White Womens Shoes Size 8Puma CLYDE GCC - Black - WomensASICS GT-1000 4 RUNNING SHOES / MULTI COLOR ( SIZE 7 ) WOMEN’S , Nike Lunar Skyelux Grey Pink Orange Women Running Shoes 855810-004 Size 8.5 , New Reebok Womens R Crossfit Nano 6.0 Pacific Cross Training Shoes Size 5PUMA BASKET CLASSIC Women Sneakers (10 M, WHITE) , Clarks Women's Tilmont Ivy Oxford , Puma Basket Heart Copper / Rose Gold trainers shoes US women's 8 Eur 38.5 , Women's New Balance 844 Size 10 B (10 medium) Walking Shoes - Brand NewNEW Rockport U72775 truWALKzero II Mesh Wingtip Shoe, Women's Black - Choose Sz , New Balance Womens - Bone Walking Shoes Size 7.5 (352119) , Nike 806559-401 Zoom Rival Track Racing Shoes Baby Blue Womens 7 ,
"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."