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.Capezio Fan Shell Combination Item Woman’s Shoes. Made In U.S.A.N.Y.L.A WOMEN'S SCOTTY FASHION CASUAL FLAT SHOES,BLACK-PA,US SIZE 6.5,MEDIUM,NEW , Land's End Women's Loafers, Size US 8.5 M, Black Leather Slip on Shoes , XHILARATION BROWN & BEIGE FLORAL SLIP ON SHOE-TARGET BRAND SZ 7 TENNIS SHOE � , Anne Klein Aricia Bow Toe Ballet Flats 691, Wine Multi, 7.5 US , Lucky Brand Emmie Round Toe Ballet Flats 929, Sable, 9 US / 39 EU , EUC Taryn Rose Kelsey Black Shoes Wedge Microfiber and Leather SZ 37G by Guess Citti Women's FLATS Light Pink , NIB ORTHOFEET Orthotic 827 SPRINGFIELD Spandex MARY JANE Black Women's Sz 5.5 M , Alfani Women Flats Shoes Juxton Black Sapphire Color 6.5 MSalvatore Ferragamo Pink Perforated Almond Toe Flats Size 9 - Made in Italy , Puma Asha Alt 2 Gray Purple Ballet Flats Slip On Sneakers US Women Size 8.5ARA WOMENS BLACK SUEDE LEATHER GORE-TEX SLIP ON SHOES 6.5 US 10 NEWNEW Naturalizer Leo Black Leather Slip on Comfortable Casual ShoesSKECHERS Reggae Fest Boots-Women's size 7.5 Black , Qupid Womens Oval-01 Leather Low Top Slip On Fashion Sneakers, White, Size 5.0 G , Womens Shoe One Star Pink Canvas Converse Running Walking Sneakers Size 5New! Under Armour Womens Micro G Torch Basketball Shoes-Style 1256436-002 89E la , Converse Low Top Canvas Sneakers Black and White Cheetah Print Women's 11 Mens 9Womens sz 11 M Nike Zoom Structure +16 16 Running Shoes Purple Sneakers Training , Under Armour Womens Gray Walking Shoes Size 9 (10537)$150 Reebok Question Mid Teyana Taylor T Women's Basketball Shoes Red Ice BD4487Scholl Orthaheel Empire Womens Comfortable Supportive Active Shoes , Basket MAMZELLE XOULO balerine compensé sandale plateform derby CUIR 40 NEUF , NEW ADIDAS STAN SMITH CF W (S81389) ADIDAS ORIGINALS CASUAL SHOES SNEAKERSNew Balance Women's W680V3 Running Shoe , New Balance Women's WF616 Fitness Shoe - Choose SZ/ColorNew Nike Womens Air Zoom Pegasus 33 Shield Run Running Shoes 849567-400 Sz 5.5 , DC Women's Danni TX SE Shoes Size - 10Lauren Ralph Lauren Women Mesa Boots US Size 5.5 B ,
"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."