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.VANELI SPORT Brown Patent MOC CROC Loafer Toggle Shoe US Size 7 COMFY SPORTYMossimo Women's Brown Animal Print Textile Slip On Ballet Flat Shoes US Size 6Keds shoes Women's size 8 1/2 White New without tagsLucky Brand EMMIE Women's Brown Leather Round Toe Ballet Flats Size US 8.5 MPrivo By Clarks Black Mary Jane Shoes. Size Women's 8.5 M Athletic Travel F , Women's Clarks Bendables Brown Leather Casual Loafers Size 9 M , NEW JESSICA SIMPSON RED WHITE BLUE WOVEN FABRIC ELASTIC HEEL STRAP FLATS SZ. 8.5 , See by Chloe Black Leather Zipper Bow Detail Elastic Ballet Flats Size 9 M , NEW Rockport M76026 XCS Rock On Air Slip-On Shoes, Women's Navy - Choose Size , Rockport Penfield Cobb Hill Collection Black Leather Zip Shoe , Skechers Womens Bikers-Knit Happens Sneaker- Pick SZ/Color. , New Soft Style Womens Fairfax BordeauxFauxTweed Fashion Shoes Size 7Puma Speeder Womens Sneakers 7.5 Gray Leather Running Gym ShoesWomen Athletic Running Casual Shoes Wedge Mid Heel Pumps Black Comfort A2775TEVA Women's Water Sport Mountain Games Vail Red Athletic Shoes 10.5M , Pin Up Couture Women's Secret 15 , Gianni Bini Women's Shoes Size 7.5 M Black Leather Plate Form Pumps Slim HeelsNike Zoom Pegasus 32 Black/White 749340-001 Running Shoes Sz 10 , Womens Nike Air 2003 Running shoes sneakers 306310 171 US 8.5 , Winter Cotton Slippers Men's Flat Indoor Slipper Shoes Pure Color Warm SlippersEtnies Womens Corby Red Athletic Shoes Size 8 (264558) , Women's Nike Shox NZ Running Shoes Navy-White-Teal Size 6Y US 38.5 EUR , Reebok Women's Trainflex Cross-Trainer Shoe, White/Skull Grey/Metallic SIZE 7.5Women's ed hardy shoes size 10 Elegant Athletic ShoesNEW IN BOX New Balance W880GP3 Women's US 7//White/Green/Purple 880*New Womens Nike Free TR 7 Reflect Trainer Shoes AA2238-100 sz 9.5 White Glacir , Skechers Sport Women's Dreamstep-Enliven Fashion SneakerVans Sk8 Hi Moc (Suede) Monks Robe Brown- Women's 5.5 , Skechers Burst Midnight Garden W/ Air Cooled Memory Foam , AVON CURVES FOR WOMAN GET BOLD SNEAKER Size 8 Medium ,
"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."