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.LIFE STRIDE Women's Fancy On Shoes, Size 6, Black Pre-owned VERY GOOD CONDITION , Muk Luks Women's Erin Mary Jane Loafer, Blue Nubuck, 10 M US , Sperry Top-Sider Bluefish Women's Boat Shoes Dock Beige/Tan 2 Eye Sz 6MTopshop Ali D’Orsay Fluffy Black Flats Size 39Jutti Indian Women Shoes Wedding Flip-Flops Khussa Pointy Flats Silver US 5-8.5 , Dansko blue/black leaf marbled Classic Clogs US 6.5 7 (A05)Mark Lemp Classics Womens Zuzu Peep Toe Ballet Flats White Size 10.0 KQJ3 , Klogs NATALIE Clogs BLACK OILED Leather Display Model Shoes 8 MNAOT LEATHER MARY JANE SHOES BLACK SZ 39~EXCELLENT , Marc Fisher Ventia Strappy Flats 434, Ivory Leather, 8.5 USTsubo 8 Womens Black Leather & Suede Oxford Walking Shoes 7 EUWomen's Authentic B.U.M Equipment Water Hiking Sandals Shoes Size 5,Gray/Blue , Nike Dart 12 Running Shoes Black Pink Womens Size 7.5 Wide , NEW Womens Tennis Shoes Size 9 Silver Blue Athletic Sneakers Walking Running Gym , Cute PLAID converse all star chuck taylor low tops size 4 / Women's 6 , Butterfly Twists Women's Robyn Ballet Flat, Black, 7 M USNew Pearl Izumi Womens Em Road H3 Running ShoesAsics Gel Womens GT-2000 4 T656N Running Shoe Sz 10.5 US 42.5 EU Dynamic Duomax , Skechers On The Go 600 Venture Navy Grey Men Sports Sandal Shoes 55366-NVYOn Cloud Womens Cloudflyer Purple Running Shoes Size 7.5 (358875) , CURVES FOR WOMEN 10 M Sandals Gray Blue Walking Toner Rocker Shape Up Slingback , mizuno wave rider 17 size 10 women , New Balance 550 v2 Women's Sz 8 M Running Walking Sneakers Shoes Gray (E2)Womens NIKE Blue Leather High-Tops Sneakers Shoes Size 10 , New Balance W990NV3 Women's Everyday Running Shoes, NavyBrand New Women's NEW BALANCE Zante Fresh Foam Running Shoes SHIP FREE US FASTNike Flex Supreme TR 5 Women's running shoes 852467 003 Multiple sizes , NAOT WOMEN'S MARY JANE COMFORT ATHLETIC Work SHOES SZ US 7Skechers EZ Flex Shoes Walking Athletic Memory Foam Air Cooled Black 6.5 7.5 8.5 , Saucony Women's Guide 9 Cobalt/Coral/Blue Sneaker 6.5M
"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."