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.02-2989 Nine West Women's Anemone Leather Pointed Toe Flat, Black SZ 7.5M , BCBGENERATION Tilda BLUE Leather Ankle Strap Closed Pointed Toe Flat Sandal 8MPALLADIUM Kassel Distressed Leather Mary Jane Women's Shoes Sz 10/41CLARKS Womens Jocolin Myla Fabric Closed Toe Slide Flats, White, Size 7.5Bass Women Bea Faux Leather Casual Slip-On Penny Loafers Cocoa Size 6 MKlogs Camila Women's Leather Clogs Display Model Shoes Coffee 8 WAnne Klein Womens Noris Leather Square Toe Loafers , Dansko Brittany Black Suede Clogs Women's Shoes Size 9-9.5 AL4622Stuart Weitzman Black Perforated Suede Pumps with Buckle Size 7.5 N , Nine West 25025320 Womens Marie Ballet Flat W US- Choose SZ/Color. , B35 Hint Slip-On Sneakers 025, White, 8 US , Women's Athletic Shoe Outdoor Casual Running Sneakers Breathable Sports Shoe LotDakota Quad Comfort J-Step ATCP Anti-Slip Oxford Women's Black Shoes 7MReebok BLACK SHOES WOMENS SIZE 8 1/2JULIETTE-3-13 WOMEN BEJEWELED SATIN SNEAKER ELEGANT LT GREY , Retro Roman Womens Hollow Shoes Black Strap Buckle Pointy Toe Leather Flats SizeMen's UNBRANDED brown w white faux fur Slip On Loafers Casual Slippers Shoes NEW , NEW Genuine Real Sheepskin Lambskin Shearling Leather Men Slippers 9-9.5, 43 , Nike Zoom Womens ArchTech Shoes Suede Running Cross Training Brown Size 7 , Nike ID 5.0 Silver green and pink Women's Size 11? , CONVERSE ALL STAR SNEAKERS WOMENS SHOES SIZE 8 HI TOP AMERICAN FLAG STARS STRIPEPUMA Women 5.5 M Cell Riaze Heather Cross-Trainer Running Shoes Steel Gray Black , adidas Alphabounce EM W White Gum BW1196 Men Running ShoesNew Balance 530 Floral White/Black/Grey Size 7 W530TCB New W/ Box Free S/H! RareNew Balance Women's Vazee Prism V2 Running Shoe - Choose SZ/ColorSketchers Shape Ups Shoes Womens Size 8 White Sneaker Walking TonerSatin Platform White or Pink Sneakers , Skechers Sport Revv Air Grey and Neon Green Sneakers Shoes US10 EU40 SN12266 , NIKE AIR MAX DESTINY BLACK WHITE WOMEN SHOES NEW WITH DEFECTS SIZE 11.5 , Newton Running Kismet II Pink, Green Women's US Size 8 (D2,2)
"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."