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.Rockport Total Motion Trutech Women Heels 2 1/2" Pumps Shoes Size 6.5 BX1790 , Airwalk Brown Suede Faux Fur Slip-On Slippers Shoes 9 , 02-509 BLOWFISH GLO NATURAL COZUMEL LINEN WOMEN'S SIZE 9Privo by Clarks 75767 Brown Nubuck/Leather Low Back Slip On Loafer Shoe 7.5MBlack Shiny Lady's Girl's Flat Slip On Low Heels Shoes US 6 / 6.5French Sole New York FS NY Womens Shoes Sz 38 Oriole Penny Loafer Orange ZEl Naturalista purple Iggdrasil Clogs Mary Jane Womens Shoes Size 42 US 11 , KS35 Fawna Square Toe Wedge Loafers, Black , Ryka Tensile Black Leather Fisherman Bungee Slide Mule 6.5 W SALE NEWNaturalizer Women's Size 8.5N Kana Tan Leather Round Toe Flats , EUC BORN Women's Shoe Clog Mule Slip On Buckle Accent Brown 8 M 39 #W965514Mephisto Cool Air Women's Patent Leather Mules, Size 9Puma Women's Caroline Wedge Fashion SneakerEARTHIES HANOVER WOMENS NAVY BLUE LIZARD EMBOSSED LEATHER FLATS SHOES 8 NEW , FRYE Clara Campus Womens 11 M Brown Leather Clogs Slip On Mules Boho ShoesMerrell Silver Lining Flip Flop Outdoor Shoes Size 11 Women's Select Fresh Grip , Casual Floral Womens Slippers Slingback Womens Slip On Pointed Toe Leather Shoes , 2017 New Womens Floral Embroidery Pointy Toe Loafers Slip On Flats Date Shoes SZJeffrey Campbell Ibiza Reagle Blue Suede Ballerina Flats Front Design Size 8DANSKO 37 ITALIAN PRO CLOGS WORK TAPESTRY & LEATHER CLOGS WOMENS SHOES , DESTOCKAGE PANTOUFLE @ MULES FOURREES MARQUE RONDINAUD @ TAILLE 42 @ NEUF , PIERRE ROCHE Mens Hook & Loop Pull On Indoor Slippers Cushion Shoe US Sizes 8-12Women's Converse Burgundy One Star Size 5.5 Red 541206FT SP16 , Mizuno womens gray purple navy Wave Rider 19 running shoes 9 M EUCSkechers Womens Multi Color High Tops Size 8.5 MLauren By Ralph Lauren Womens Jolie Fashion Sneaker Blue Stitched Size 9.5 MWomen's Vero Cuoio Flats 37 Reliable Performance Flats , Adidas Terrex Tracerocker Womens Blue Walking Camping Shoes Size 7.5WOMEN'S NEW BALANCE W530BAC CLASSICS TRADITIONNELS RUNNING SHOES SIZE 8.5 , Skechers Shape Ups Sneakers - Womens Size 10 - Gray/Silver/Pink - 11806
"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."