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.NORTHSIDE Womens KAYLA Black Waterproof Rubber Slip-Ons US 6 (913004W001) , Giani Bernini Womens Black Leather Loafer Shoe - Size 6M , CROCS MALINDI FLAT SLINGBACK WOMENS BROWN US SIZE 4 M NEW WITH TAGSTROTTERS Navy Blue Woven Leather Flat Slip On Loafer Shoes Liz Women's 7*NEW* Hush Puppies Red Leather Mary Jane Comfort Shoes Women's Size: 7.5 W , Miu Miu Mule Kitten Blush Slip On Size 8 9 Pointed Toe Suede Slippers Heel , Born BOC Concepts Peggy Clogs Shoes Black Patent Leather Women's US Size 7 MBørn LADIES BROWN LEATHER UPPER INNER LINING BROWN CASUAL CAREER SHOES SIZE 9M M , Dr. Scholl's Women's Madi Mules - Size 6.5 M, BlackMarc By Marc Jacobs Black Flats Size 38,5 , Isaac Mizrahi Live! SOHO Quilted Slip-On Sneakers pick size colorJ.G. HOOK Patent Leather Classic Oxfords Dark Brown Women's 7.5 M 38Betta Carrano Rustic Orange Suede Round Toe Ballet Flats Size 36 6 , STUART WEITZMAN Brown Perforated Suede Chain Wedge Loafers (Size 8.5 M)Mizuno Women's Wave Lightning Volleyball Flat Shoes Size Us 8 / Eu 38.5 Black , sport shoes dc skateboard court graffik se -- size 7 w -- burned outsoles - newNew Fashion Women Canvas High Platform Pull On Fashion Sneakers Casual Round ToeWomens Flats Buckle Strap Pointed Toe Mules Slippers Casual Loafers Shoes A-111Nike Free Running Shoes Women's Size 8 , New Asics Gel Contend 3 training shoe Womens size 6.5 Silver/TealGuess Jacaly White Womens Shoes Size 5 M Fashion Sneakers MSRP $69 , Pearl Izumi Womens Tri N1 White Running Shoes Size 9.5 (425071)Hoka One One W Clifton 3 Running Shoe Women's Size 8 Blue Orange , NEW NIKE WOMEN'S AIR MAX THEA 599409 007 BLACK Sz 5.5New Balance WW928WB2 Women's Walking Shoes White/Blue New in the Box , Puma x Fenty by Rihanna The Trainer High White - Womens - Size 10 BNIB New Balance Womens W775v2 Running Shoes Lightweight Trainer Sport Cush 6-11MNIB NEW BALANCE WOMEN'S WS 215 RC LIFESTYLE SNEAKERS PINK SIZE US 6 90$ , K-Swiss The Classic Lite T (Stingray/Cloud) Women's Tennis Shoes - Size 5 , Under Armour Womens Blue Running Shoes Size 7 (403947) ,
"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."