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.NISOLO Oliver Oxford Noir US Women's 6.5 EUCLands' End Women's Blue Leather Slip On Low Wedge Clog Shoes US Size 7.5 B , Rocket Dog Women's Chow Chow Lucky Sneaker, White Cotton, 8.5 M US , Daisey Fuentes brand women's lavender suede loafers, 7.5 M, 1 in. heelClarks Women's Slip on shoes 8m pewter leather in motion comfort work casual , COLE HAAN WOMEN'S GREEN SUEDE LOAFER SHOES 6-1/2 B ITALY 6.5 , AREZZO Navy LEATHER Patent Trim Red Bow Snout Toe Flats MADE IN BRAZIL Sz 7 , Merrell womens petunia brown mary jane suede wedges size 6 , BOC BORN Womens Slip-On Closed Back Comfort Clogs SIZE 8.5/40 , Crocs Womens 11 Black KARIN Classic Sling Back Mary Janes VGC , Dr Scholls Shoes Womens 9M Leather MaryJanes Cushioned Insoles Beige Comfort , CALL IT SPRING Thirenia Women Slide Sandals (6M, Peach) , Vaneli Womens shoes Size 8M Styled In ItalyKelly & Katie Womens cigola Closed Toe Loafers, Black, Size 10.0 UQ0q , Caleco Slide Mules Bats Size 40 9.5-10 New , SoftWalk Women's Napa Ballet Flat, White, 7.5 N USAlfani Womens Perrlla Fabric Pointed Toe Slingback Flats , NIKE FLYKNIT LUNAR 3 Purple WOMENS RUNNING SHOES SIZE US 7.5 SH23Authentic Fenty Black Puma Empty Shoe Box Black 15 X 9.25 X 5.5" , womens size 8.5XW XE NIKE ZOOM VOMERO-12 GREY/HOT PINK SNEAKERS $140 , Skechers GO Walk Joy Slip-on Shoes Radiant Navy 9W NEW A302183Propet Women's Stability White Walker Sneaker 10.5W , Nike Revolution 3 Women's Running Shoes Hyper Pink/ White/ Black Size 9.5(US) , RYKA Ryka Womens Grafik Flow Cross Trainer- Pick SZ/Color.New Balance Women's 580 NB Grey Shoes Grey with Silver 5 B , Converse Chuck Taylor All Star Hi Womens Sneaker Midnight Navy 557938C Size 7.5 , PUMA Women's Rebel Mid WNS En Pointe Sneaker, - Choose SZ/ColorReebok Women's CL Lthr Sneaker, Us-White/Gum, 8 M USWomen's ADIDAS CLOUDFOAM ADVANTAGE Black Athletic Casual Sneakers AW4288 NEW , Rockport Prowalker nubuck sneaker shoes 8M
"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."