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.KEEN 1011401 Presidio Women's Casual Shoe SZ 7 , Womens Sperry Top-Sider Leather Green/Yellow/White Slip Ons Size 7M EUC!! , TALBOTS Women Wingtip Ballet Flats Size 6.5B Red Brown Leather , NATURALIZER LADIES BROWN SUEDE LEATHER FLATS SHOES SIZE 7 MPrivo by Clarks 9 M Burgundy Suede Cross X Strap Mary Janes Loafer 76467England HOTTER 'Helium' Women's Size 9.5-10 Black Suede Leather Slip-On LoafersNWT Frye Leo Ankle Wrap Leather Women's Espadrille Flat Sandals Navy Blue Sz 5.5ALEX MARIE Navy Blue Open Peep Toe Buckle Strap Kitten Heel Sandals Size 6.5MFINN COMFORT Black Patent Leather Adjustable Shoes Womens Size 4.5 US 2 UK Exc. , Klogs Marisa Women's Clog Shoes Display Model White 11W, Euro 43.5ZARA WOMEN (6.5/37) BURGUNDY SATIN FLAT SLINGBACK wGEM BUCKLES Sz 6.5. 37 BNWTCHAMPION Slip on Shoe MEMORY FOAM Pink women sz 5.5 medium , Zapatos Botas Botines de Mujer Para Vestir Casual De Moda Elegantes Botas , Nine West Soto Women's FLATS Dkr/DkrClarks Collection 16180 Cushion Casual Stitched Slip on Flats Women Brown US 8WSkechers Goldie - Diamond Darling Silver Womens Fashion Sneaker Size 6.5MWOMENS SKECHERS SPORT MEMORY FOAM RUNNING/TENNIS SHOES SZ 5 purple galaxyDiesel White Leather Running Sneakers Womens Sz. US 8New Balance 643 All Terrain Womens Hiking Shoes Beige Tan WW643TB Size US 7.5 , DR SCHOLLS WOMENS ATHLETIC SNEAKERS SHOES SIZE 9.5 GEL CUSHION COLOR GRAY CASUAL , ASICS GEL-Contend 3 Running Shoes-Women's size 7.5 GreyPuma Women Solange Suede Classic SneakersEllie Women's Petra-567 Gold PU Size 6 MWomen's keds women's tennis shoes Great Varieties Athletic ShoesAsics Gel-Zaraca 5 GS Purple Coral White Kid Junior Running Shoes C635N-3606 , NIKE WOMEN'S AIR FORCE 1 HI PREMIUM SNEAKERS LT BONE/WHITE 654440 004 SIZE: 7.5Classic Converse Chuck Taylor Lows | Exclusive Pepsi Blue| Women's 7, Men's 5ASICS Women's Gel-cumulus 17 Running Shoe, Silver/Hot Pink/Turquoise - Size 9.5 , Skechers Black Glider Stunner Flat Knit Slip on Sneakers 8.5 Sale , Womens High Top Canvas Shoes Casual Comfort Sneakers Ankle Boots Christmas Print ,
"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."