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.LeSportsac Womens Provincetown Ballet Flats Shoes Size 6.5 Gray Polka DotCole Haan NikeAir D37070 Women's Ballet Flats, Size 6 BWomen's Lacoste Sport Mary Jane Pink Slip On Flat 9.5 Ballet Leather Ballerina , Soft Walk *Lafon* Womens Mary Janes Size 8.5M-Black LeatherFFC New York Woman Two-Tone flat shoe, multi-color orande/tanFranco Sarto Womens Porter Leather Closed Toe Mules Black Size 10.0 2I0T , NEW B. Makowsky Paint Women's Round Toe Leather Ballet Flats Shoes Sz 6W , BETSEY JOHNSON Women's 7.5 Rounded Toe Flats Velour Blue Felt Shoes NEVER WORN , Womens sz 7 M Born Masia Black Patent Leather Copper Ballet Flats Shoes Cap Toe , Isabel Marant Etoile Black Pony Hair Leather Bow Moccasin Flat Shoe 36 6 , VANELi Women's Seana Black Fabric and Patent Ballerina Flat , Gingham Ankle Wrap Flats Size 6 1/2 J Crew Navy , Eastland Rosy Black Patent Leather Oxford Sneakers Shoes 7.5M 7.5 MSRP $89Nike Women's Solarsoft Thong II Thong Flip-Flops Sandals sz 10 488161 161Women Lady ALL STARs Chuck Taylor Ox Low Top classic Canvas Sneakers Gray us7.5Purple Geometry Hi Tops Canvas Shoes Women Casual Sneakers Breath Cool Trainers , New! Womens Skechers 22602 Gratis Shake It Off Slip-On Shoe GRY (Wide Width) C57 , Nike Women's Rosherun Hi Sneaker Boot, Size 5, New , Nike flex experience RN 5 running shoes. Size 8.5 , Women's Converse Chucks Monochrome 159542c Rosa Carmel, Delicate Athletic Shoes , WOMEN'S SHOES SNEAKERS ADIDAS VS CONEO QT [DB0131] , NEW New Balance WW928BK2 Black Leather Women's Walking Shoes Size 13 - 4E Wide , KEEN Womens Green Hiking Shoes Size 5 (14790) , Adidas x Rita Ora Women's Tech Super - Silver/Blac US sizes : 7; 7.5; 8; 9; 9.5Ak Anne Klein Fashion Sneakers Sz 8 1/2 , Womens ADIDAS ZX FLUX NPS 2.0 W Grey Trainers B34008VANS ISO 1.5 (Moroccan Geo) Classic White UltraCush Trainer MEN'S 7.5 WOMEN'S 9 , Reebok Classic Club C 85 Zip Shell Pink/Chalk Women's Tennis Shoes BS6606 , Bearpaw Meadow Apres Boot - Women's Hickory 8.0Adidas Womens Ortholite Performance Running Shoes Sz 5 Vigor TR 6 Sneakers New
"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."