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.New women's ballet flat ballerina loafer mix color casual work black purple grayAthena Alexander Women's Lucille Ballet FlatSAS Shoes Ladies Size 9 Narrow Black Suede , Women's Easy Street Black Leather Sportster Slipon Shoe w/Back Straps SIZE 10MEspadrilles Summer Beach Shoes size 5 , Traditional Indian Handmade Women Shoes Leather Slippers Loafers US 5.5-9.5 , SAS Womens 7.5 WWW Extra Wide Shoes Comfort Casual Black Adjustable WalkingTraditional Women Shoes Mojari Handamde Jutti Party Wear Oxfords Flat New US 9.5 , SANUK LAUREL SAGE GREEN SIDEWALK SURFER SHOES, SIZE US 7/ ~NWTManon Womens Flat Low Heels Flatform Loafers Ladies Slip On Shoes Style Size New , Soludos Denim Smoking Slipper Espadrilles Sorry Not Sorry Embroidered Sz 6 Flatschaussures COULEUR POURPRE poil de poulain camouflage 36TOD'S YELLOW PATENT LEATHER SHOES SIZE: Eu 39 Us 8 MADE IN ITALY , Women's Skechers Bikers-Tranqility Casual Shoe- 21285/BBKPropet W3840 Washable Walker Walking Comfort Diabetic Oxfords Women's US 10EE , Ecco Mary Jane Ankle Hook & Loop Strap Leather Sandals Size Us 8.5 Eu 39Keds Slip On Sneaker White Canvas Mules Women's Us size 6 Eur size 36 L2-CH17 , Womens Topshop Turin Black and Gold Metallic Elastic Trainer Sneakers Size 10.5 , Women's Basket femme Longsdale 36,5 Carmel, Delicate Athletic ShoesASICS Womens Gel-Fit Tempo 3 Cross-Trainer-Shoes- Pick SZ/Color.ASICS FUZEX RUSH T768N 4349 DIVA BLUE INDIGO WOMEN SHOES SIZE 8 & 10Women US Shoe Size Athletic Slip On Memory Foam Casual Lightweight Sneakers NavyVans Women Classic Slip-On Mule - Leather black black VN04KTL3B , Inov-8 Womens Race Ultra 290 Running Shoe Raven Ocean Size 11 B US , Dolce Vita Tina Sneaker, Women's Size 7.5, Copper , adidas Neo Courtset Cooper Core Black Metallic BB9657 Women Size 7 , Nine West Onyeka Round Toe Slip On Sneakers, Black/White, 6 USNew Balance 501 Running Shoes Athletic Purple WL501SS3 3F-8 Women's 8.5 B , Cole Haan Velcro Sneakers/ Shoes Size 5.5Women's Reebok Classic Black Leather Walking Sneaker Size 9.5 - New ,
"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."