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.Sperry Topsiders with Houndstooth Trim size 7 1/2 , Lucky Brand Emmie Women's Pewter Silver Leather Ballet Flats Shoes US Size 5.5 MEasy On Boat Shoes Street Style Sneakers Flats Pink w Gray Polka Dots Women SizeEasy Slip-On Casual Canvas Shoes w/Front Tie Up 5--8--9.5--11 , Tory Burch MISMATCH Womens 9 8 M Reva NEW $235 Patent Leather Flats Shoes fhClarks Kinzie Light Ballet Flats 293, Black Combi, 8 US / 39 EUWomen's Sporto Jessica Black Comfort Active Mule Slip-On Shoes Size 7 1/2 , Katy Perry Women's The Kyra Ballet Flat, Blue, Size 8.0Juicy Couture Women's Palm Tree Slip-On Sneakers Shoes 7 white blue JCNICKYPALMEastland Newbury Clogs - Women's Size 9.5 M, BlackJLY041 Hudson Ladies Faux Suede Diamante Front Casual Espadrilles Flat Shoes , Frye Women Size 9 Flats Regina Ballet Tan Beige Snake Skin Point Leather TasselFitflop Loaff Suede Clogs Timberwolf Women’s Size 9 M , New Balance 813 Women US 6.5 Gray + Pink + White Cross Training Shoes WX813 , REIGN! Soda Women's Comfort Casual Slip-On Loafer Walking Fashion SneakersDansko Ann Nappa Slip Ons-Women's size 9.5-10 BlackRyka Carrara Insignia Blue/Elsa Blue/Yucca Mint Women's Size US 6 WMerrell Siren Hiking Shoes Vibram Women’s Size 6 M US Excellent ConditionNew New Balance Womens Wprsmpr Purple/White Running Shoes Size 5 (C,D,W)NIB UNLTD BY MARC ECKO PHEROCIOUS SNEAKERS SKATEBOARD WHITE/GOLD WOMENS 8.5 , Grasshoppers Women's Jade Twill Fashion Sneaker, Black, 7 N US , Asics Woman's Gel Kayano 22 Running Sneaker Shoes Navy Blue/Pink Size 8 T597N , Fenty Puma By Rihanna Women Bow Creeper Sandal Silver Pink 365794-01 Size 8Nike Women's Air Huarache Running Shoes Ember Red White 634835-801 Size 6.5 NWOB , CHACO Kanarra INDIGO Blue CROSSOVER Shoe SNEAKER Women's Sz 7.5 STREET Hiking , ASICS Womens Gel-Nimbus 18 Gray Running Shoes Size 7.5 (AA) (361515)Propet Stability Walker Walking Shoes, Women's Size 7.5 N, Black , Reebok Women's Runner 2.0 Mt Ankle-High Running ShoeNike Blazer Mid GS Casual Kids Youth Shoes Black White 895850-001Skechers Women's Shape Ups Black/White Fitness Walking Shoe Size 8 11809 ,
"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."