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.Sperry Top-Sider Bluefish 2-Eye Unisex Youth Linen/Oak Boat Shoe 2M , 8.5 M Naturalizer Tan Suede Beige Slip-on Shoes Flats comfort walking casual , Aerosoles A2 Women's Envelope Flat Grey Fabric Size 10.5Propét WOMENS BROWN SANDALS SHOES FLATS SIZE 6.5 1/2 M EXCELLENT ANKLE STRAPWomen's SAS Simplify Loafers Shoes Size 12S Black Leather Horsebit Tripad AC15SH16 Munro American 7.5N USA Brown Leather Embellished Monk Strap Loafer Shoes , Dansko Leather Wedge Unique Flats loafer Brick Red SZ 9 M Super comfortable , TROTTERS Women's Black Patent Leather Slip On Loafers Size 7.5Calvin Klein Women's Idella Black Nappa Two Tone Patent LeatherMix No 6 Womens ERICIA Fabric Closed Toe Ballet Flats, Black, Size 6.0 MSRXClarks Brown Leather Slip On Loafers Slides Flats Shoes W/ Buckle Women's 7 M , Anne Klein Women's Daneen Navy Leather Slip-on Loafer , 318)SAS ME TOO Tripad Comfort Diabetic Walking Women’s Shoe Sz 10 N Mocha BrownCole Haan Womens Weldasam Closed Toe Ballet Flats Blue/Black Size 6.0Ralph Lauren Womens Belen Leather Closed Toe Loafers, Eggshell, Size 5.0 9TvT , Mocassins MASSIMO DUTTI Tout Cuir Camel T 40 TRES BON ETATBetsey Johnson Women's Hazyl Flat, Black/White, 9 M US , KIRRILY JOHNSTON sz 7 womens Leather sandals / shoes RRP$300+Nike Shox Navina 2010 Gray/Blue Womens Sz 8.5 US Athletic Running Training Shoes , NEW BALANCE 749 Women US 9.5 D White /silver/navy Blue Athletic Running Shoes , NIB WOMENS VANS ELBA SKATEBOARD SNEAKERS - BURNT OLIVE - SIZE 5Reebok Royal Lumina Fitness Women's ShoesBZ522 2 STAR shoes gold textile women sneakersTretorn Women's Nylite18Plus SneakerNEW Converse Missoni Chuck Taylor All Star Shoes Pink Black 154441C Sz 9.5 11.5Nike Womens Air Scandal Mid 330238-112 White/Metallic Silver Size 8D'lites Skechers Black Silver Shoes Women Sport Casual Comfort Memory Foam SZ 7 , TEAM ADIDAS GOODYEAR Brown Pink Suede Women's Casual Driving Sneaker Size 7.5 , The North Face Ultra MT Women's Black & Purple Running Shoes Size 10 , COLUMBIA Orange White Mint Women's Size 7 Textile Upper Sneakers Walking Shoes
"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."