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.02-712 Women's Sperry Authentic Original 2 Eye Boat Shoes SIZE 8.5MCole Haan NikeLab Women's Slip On Cross Strap Orange White Slip On Shoes Sz 7.5I LOVE COMFORT BROWN SHOES WOMENS SIZE 6 1/2 M STYLE 86009 , NWOB Real Tree Girl Wren Loader - Size 6 - 70% off , womens shoes Naot brown leather size 7/38 , Ladies Shoes Spot On F80108 Black UK Sizes 3 x 8 (R10B)Sperry Top-sider Woven Leather WovenQuilt Gray Silver Boat Shoes Women's 9 M , DAVID TATE women's slip on black suede shoe size 10W wide loafer NICE , MERRELL Barrado Brown Suede Womens 7.5 M Comfort Slip On Zip Light SportLucky Brand Bapsee Light Blue Denim Multi Slide Mule Slip On Flat 11 , Dr. Comfort Laura 3303 Women's Shoes 6W , Sam Edelman Felicia Ballerina Red Suede Flats Slip On Shoes Women's 7.5 M$129 Talbots Women's Edison Brushed Twill D'Orsay Flats 9 1/2 M NEW w/o BoxLucky Brand LK-Organza Black Nubuck Mule Block Peep Toe Heels Women's Size 6.5M , Penny Loves Kenny Women's Koi Fashion SneakerNWT Women's Sperry Top-Sider Seacoast Gray Silver Shoes Loafers - Size 7 M , GRAVATI Women's Shoes Brown SUEDE Loafers size 8 US , Klogs Piper Womens Clog Shoes Display Model Partridge Beech 6.5 M , DANSKO DEE COBALT WOMENS BLUE/TEAL STRAP OPEN TOE CLOG SANDALS SZ 8.5Puma Womens Carson 2 Molded Black Running Shoes 5.5 Medium (B,M) BHFO 6805xx ASICS GEL EXALT PURPLE ATHLETIC WOMENS 8.5 MCapezio Dance Women's Jr. Footlight W - 550Nike 831562 Womens Zoom Winflo 3 Low Top Running Training Shoes SneakersNike Zoom Rival Waffle Women's Binary Blue/Hot Punch/Polarized Blue 04719406Adidas Original Women's Stan Smith (S82258) Athletic Sneakers Suede ShoesNike Women's Flex Experience RN 5 Anthracite/Pink Running Shoes-Asst Sizes WIDEWomen's Vionic Gray Blue High Top Running Athletic Sneakers Shoes Size 9Ahnu Women's Yoga Flex 1010148PATL Pure Atlantis Brand New In BoxZara Woman Star Sneakers Size 6 2412/301/001 , Ladies Helly Hansen Trainers W The Korktrekker 5 Low HTXP
"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."