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.Kelly & Katie Womens zoe Canvas Pointed Toe Beige Size 7.5 3HeY , CHAUSSURE SANDALE BRENDA ZARO CUIR TAILLE 37 ESCARPIN SHOES/ZAPATO/SCARPE BELiz Claiborne Shoes Blue Green Striped Canvas Flats w/ Faux Leather Trim A251961 , Spot On Ladies Shoes F9725 Black or Burgundy UK Sizes 3 to 8 (R9A)UNIONBAY Women's Bits-u Mule, Black Patent, 6 M US , Sanuk Women's Shorty Tx Chill Sidewalk Surfer Shoes, Size 5, NWT , COLE HAAN Brown Leather Classic Slip-on Penny Loafer Flats Woman's 7B BrazilNew Women Liliana Messina-60 Leatherette Cap Toe Caged Cutout Oxford Flat Size , sigerson morrison Made in Italy Red Velvet Rhinestone Buckle Slide Sandals 6.5 , Sergio Rossi Black Suede Bow Accent Loafer Flat Shoe Size 36 6Klogs Martha Womens Clogs Shoes Display Model Leather Black 8 M , Via Spiga Lilac Ballet Flats, Coral Suede, 7.5 US / 38 EU Display , Cole Haan Purple Leather Flats Womens Size 9 , Footjoy Greenjoys women's 7 M Golf shoes cleats 48435 white blue worn onceadidas Track - Green/Black (no spikes) Cleats (Women's 8.5) - UsedFashion Women's Running Trainer Athletic Breathable Sneakers Sport Casual Shoes , Fila shoes women Size 7.5 Machu Walking black sneakers sports gym WK USED LITTLEDREAM PAIRS Men's 160930-M Lt.Grey Slip On Athletic Water Shoes - 10 M US , Rocket Dog Women's Calani Washed Denim Cotton Sneaker, - Choose SZ/Color , Puma Womens Carson 2 Molded Black Running Shoes 10.5 Medium (B,M) BHFO 2078 , New Balance WLPROPLA B Pro Court Black Suede Women Shoes Sneakers WLPROPLABNike Women's Zoom Winflo 4 Athletic Snickers Running Training Shoes Multiple... , DV by Dolce Vita Jaimee Platform Fashion Sneakers 764, Floral Print, 8.5 US , Women's VTG Vans Checkerboard Bright Purple Berry Slip-On Skate Shoe sz 9.5NWT Nike Women's Flex Experience RN 2 Sneakers Athletic Shoes Blue Pink Red 8Nike Benassi Solarsoft Slide 2 Women's Black/White 05475010Women's Nike Elite Shinsen Running Shoes NEW Crimson/Red/Sail/Blue, MSRP $80 , Nike Air Zoom Fly 2 Women Hot-Lava Black Glow Running Shoe Sz 8 EUC! , Women's Nike Dunk Sky HI Essential Sz 9 644877 101 , New Nike Downshifter 6 Women Running Shoes Sz. 8.5 - 684765-002 ,
"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."