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.C Label Women's Randy-7A Black Slip-On Loafers 7.5M , LADIES WOMENS VINTAGE TASSEL LOAFERS FLAT SCHOOL OFFICE SHOES PUMPS BROGUES SIZE , Womens Keds Canvas Label CH DipSupreme by Softspots 7.5 brown Mary Janes womens fisherman sandals flatsNEW NWT! VINTAGE Leather CRAFT PREMIER WHITE Hurache Sandal Shoes Women SZ 6Sperry Top-Sider black glitter SHOES WOMENS SIZE 8 MWomens 7M Duck Shoes Aquaduck Skimmers Sail II Vegan Lavender/Lt Brown Excellent , New Eddie Bauer Might Women Red Canvas Slip Shoes 9 , Hotter Women's Mabel Navy Blue Canvas Sneaker Shoes Size US 7Cole Haan Monroe Penny Argento Reflect Size 5 Women’s Loafers , Franco Sarto Womens L-Bocca971 Square Toe Loafers Black Calf Size 5.0 ezzEKaty Perry Women's The Kyra Ballet Flat, Pewter, Size 8.0Ryka Orleans Navy Blue Leather & Plaid Slip-on Boat Shoes NEW , Charis Womens Flats Low Heels Slip On Espadrilles Loafers Ladies Shoes Style NewSoludos Women's Bandana Platform Smoking Espadrille Slippers Indigo MM1 Size 9 , $150 El Naturalista Womens Nokue Mary Jane Shoes, White/Tibet/Rose, 36 EU / US 6 , NIB Womens Bloch Shoes Leather Ballet Flats Size US 9.5 9 1/2 , Attilio Giusti Leombruni Women's Brown Leather Round Toe Moccasin Loafers Sz 41 , Easy Spirit Women's 'Iggy' Regular Suede Casual Shoes - Wide , Skechers Bobs- Chill Luxe Buttoned Up Flats, Women's Size 8, BlackADIDAS Neo Women's 7.5 Cloudfoam Lite Racer Navy Blue Slip On Sneakers Shoes , Dooney Bourke Womens Pebble Leather Loafers Boat Deck Tan Brown size 11 m (D1) , NIB ASICS GEL-Contend 4 T765N - Black - Womens 7.5 US , Josef Seibel Dany 05 Shoe - Women's Size 6/6.5, Wine , Merrell Outright Edge Mid Womens Sedona/Glacier SneakersAsics Gel Kayano 22 Womens Running Training Shoes Size 9 Blue Pink Green T597N , SPERRY TOPSIDER Dark Brown Size 7.5 EUC , ADIDAS DURAMO 8 W BB4671 BLUE WHITE ORIGINALS RUNNING WOMEN'S SIZE 6.5 NEW WOB , NEW BALANCE WL574ILA 574 LUAU PACK TROPICAL AQUA NEON LIFESTYLE SIZE 7 WOMENSadidas Solar Boost Running Shoes, Women's Size 8.5, Black/Coral
"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."