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.Superga Womens Summer Plaid Canvas Slip On Loafer Shoe - Size 10.5MJack Rogers Women's Regina Platinum Ballet Flat SZ 6.0 M PRE OWNED D3245 , Jutti Indian Handmde Leather Women Shoes Blue Ballerinas Flat US 6-9 , Women's Lands End Leather Shoes Slip-on Casual Mocs Casual Comfort BEIGE-10 B , Hotter Size 8 1/2 Women's Pink Strap Slip On Shoes Jl072217 , Liliana Krixie Gold Oxford Pointed Rhinestone Rimmed Platform Spectator LoaferWomens Clarks Size 9 1/2 Slip On Shoes , CLIF Paris Made in Italy 'Marie' Ballet Flats Shoes Brown Leather Size 36Klogs Women's Clogs Display Model Shoes Astra Partridge Square 9 M , ARRAY Womens Freedom Leather Square Toe Loafers, Beige, Size 12.0 4VJ6I35 Oleena Slip On Loafer Fats 578, Light Gold, 6 USWomens Merrell Circuit MJ Brown Shoes US 6 , Nike Free 5.0 black and coral sneakers, Sz 7.5 , Clarks Perforated Leather Ballet Flats Gracelin Lea Black 9.5M NEW A306040New Women PU Satin Bow Tie Low Top Sneaker - 17926 By Refresh CollectionNike Training Flex Supreme 3 Running Training Shoe Men's Size 10.5Skechers Women's Shoes Size 9 Shape-Ups Walking Shoes Light Grey Green03-115 Altra Women Torin 3 Road Running Gray/Pink SIZE 10Saucony Kilkenny XC7 Running Shoes - Women's Size 8.5M - PinkWomen's Onesole Women's Duke University White/Multi Diversified Latest Designs Athletic ShoesSkechers 23110 Black/Charcoal Air Cooled Memory Foam Slip On Walking Shoes , CONVERSE All Star HI Parchment ImpriméNike Air Zoom Pegasus 32 Print 806806-308 Voltage Green/Hyper Orange/White SZ 10 , NEW Women's Nike Air Zoom Strong Training Shoes Size 7Nike Women's Flex Contact Running Shoes Bordeaux/Tea Berry/Pink Nebula 5.5Asics Women's Gel-Contend 4 Running Shoe, White/Bay/Silver , Nike air max 90 ultra prm Women's sneakers 859522 400 Multiple sizes , adidas TERREX AX2R Women's Shoes Light Blue Coral S80915 Size 8 , Sketchers Classic Fit Air-cooled memory foam shoes, New, not in original box , Nike Air Womens Slip On Shoes Size 6 Eur 36.5 Sneakers ,
"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."