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.Bandolino Ferrista Bow Tie Ballet Flats 809, Light Pink, 7.5 US , Ann Taylor Women's Grey Glitter Slip On Round Toe Ballet Flats Size US 6 MLower East Side Brown Studded Round Toe Low 1.5 Inch Wedge Slide Womens US 9.5 MWomen High Top Canvas Round Toe College Fashion Casual Shoes Flat New SneakersLadies spot on slip on open toe shoes f0586 , Crocs Ballet Flats Womens Size 7 Brown Rubber Slip On Shoes circle holes , 9M Isaac Mizrahi Live! Bailey Loafer Metallic Taupe Patent , BARE TRAPS Women's sz 7 Red Kryland Cut Rubber Sole Ballet Flats Shoe (P) , Franco Sarto Grey Suede Twilight Studded Slip on Espadrille Flat 9.5 NEWLUCKY BRAND LP Arman Olive Green Suede Moccasins Loafers Slip on Shoes Women 8MOld Beijing Cloth Embroidered Shoes Colorful PhoenixFinn Comfort Ladies Brown Leather Sandals Comfort shoes Size 38D , Enzo Angiolini Womens libelle Closed Toe Loafers Black Size 11.0 GXne , Aerosoles Womens Elimental Closed Toe Boat ShoesSAS Classic Penny Loafers Size 9 Slim Women's Brown Leather Comfort MocsSam Edelman Paris Mules - Women's Size 11M, Black , Women's Dr Scholl's Friendly Ballet Flats Black Smooth 10WAcorn Ellsworth Suede Moc Slipper - Men'sGeorgia G050 Cedar Falls Moc Toe Slip On Full Grain Leather Moccasins LoafersSkechers Synergy 2.0 - White - WomensVans Off the Wall Womens Surf Shoes Rata Lo Tribal STV Navy Blue Flats 9.5 NWT , Skechers Women's Vaporize-Catalan-Scalloped Colar Twin-Gore Jute Wrapped Slip... , Skechers Performance Men's Go Walk 3 Unwind Slip-On Walking ShoeCharcoal11 M USWomen's Nike Lunarepic Flyknit Multicolor White 6 NEW , ASICS Alpine XT Women's Trail Running Shoe Sneaker Gray Sulfer Size 7 NEW BOXAsics Gel Quantum 360 Silver/Carbon-Turquoise T5J6N 9373 Women's SZ 8.5 , Brooks - Addiction 12 Running Shoes - Women's Size 11 D - GrayVans Womens Sk8-HI Slim Sneakers Vintage Floral/Marshmellow Size 5.5 New , Brooks Ravenna 8 Womens Size 7 Purple Pink Running Shoes K4SANUK FIONA PEACOCK SLIP ON SANDAL US 7 / / NWT ,
"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."