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.JESSICA SIMPSON Women's Black Leather Ballet Flats Shoes Size 6Dansko Women's Courtney Black Leather Mary Jane Clogs /US 9.5-10 EUC02-3529 Women's Sperry Seaside Perforated Sneaker Grey, Size 8MSet 5 mini-coussine Gel Soulagement Douleur Invisible Transparent et AntiderapenEarthies Women's 8-B Bremen Black Patent Suede Leather Slip-On Loafer Flats $140 , WOMEN'S BRAND NEW WHITE LEATHER BALLET FLATS SZ 7 1/2 BWomen's Shoes Soda Zig S Slip On Loafer Sneakers Black and White*New* , Giani Bernini Womens Jileese Square Toe Loafers Light Fawn Size 10.0 5eXGTooled Western Square Square Toe Womens Size 7.5Women's Paul Green Munchen Black Leather Toggle Oxfords US 5.5 M , Women's Ipenema Brown Leather Low Heel Penny Loafers Size 6.5 M , Trotters Womens leatha Closed Toe Ankle Strap Loafers , SKECHERS SHAPE UPS WHITE GRAY WALKING ATHLETIC FITNESS SNEAKERS SHOES SIZE 8.5 , 18 Women Furry Mules Suede Leather Bowknot Flat Low Heel Slipper Round toe Shoe , AGL Attilio Giusti Leombruni Moccasin Flat Loafer 7.5 38 Euro $298 EUC , New Womens Skechers Microburst Fluctuate Shoe Style 23304 Navy 76W pr , Converse All Star Purple WIne Canvas Side Printed Tongue Women's Size 9 / 40 EUConverse All Star 100% leather shoes 40/9 women's blackRyka Divya Training Sneaker - Women's Size 9M - Black , Women's reebok training sneakers size 9 Wear-resisting Athletic ShoesSupra Shoes 7.5 Pink Party High Top Sneakers Womens NEW , Store Rtn-Womens 8.5M/EU39 Keen Aphlex Waterproof Hiking Shoe -Plum Shark PurpleRyka Women's Intent XT 2 SR Trail Running Shoe - Choose SZ/Color , Nike Free RN GS Run Pink Blast Silver Kids Girls Women Running Shoes 833993-600STEVEN by Steve Madden Hilda Slip On Fashion Sneakers 324, Black, 9 USConverse Chuck Taylor All Star Shoreline Women Mint/White Slip On 556690F All Sz , NEW Nike Air Extreme Volley Volleyball Training Shoes WOMENS 14 White 442249 101 , BROOKS Adrenaline GTS Mogo 14th Edition Womens 9.5 Medium Blue GreenWomen's Nike Lunarglide+ 4 Purple Medium Violet Silver Running 524078-406 sz 9 , WOMEN'S SKECHERS GO WALK 4 EUPHORIC 14920 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."