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.02-2795 LifeStride Women's Sims Slip-on Loafer,SIZE 8.5M , BORN Brown Ballet Flat 8 EUCMetallic Gold Dock Shoes by Ralph Lauren NWT SZ. 8.5Sporto Jasmine2 Faux Fur Lined Slippers, Red, 7 M US Used , Liz Claiborne Philicia Gold Stone w/Buckle Shiny Loafers Flats Shoes Sz 8-1/2M , Spot On Black Ladies Slip On Dolly Shoe F8531Women's Calvin Klein Black Suede Leather Jan Loafers Size 8 M , Clarks Womens Mule Clog Shoes Size 7.5 M Artisan Collection Brown Leather Slide , BC Footwear Women's Society Exotic Ballet Flat, Black/White, 6.5 M US , Remote Control Rubber Sole Multi Color Floral Leather Loafers/Driving Shoes 5.5 , Brighton Italy Hope Women's Slip on Shoes 9.5 Leather & Fabric Loafers Lug SoleCrocs Shoes Black Ballet Slip On Flats-Size 11W-SHIPS FREE , Women's HOTTER Green Mist Gore-Tex Walking Shoes-Size UK7/US9 , Merona Women's White/Blue Striped d'Orsay Pointed Toe Ballet Flats US Size 9.5Women's New White Calvin Klein Celia Loafers Size 7 , VIONIC Ladies Blue Splendid Midi Perforated Slipon Sneaker Shoe Size 8.5US 40EU , Adidas Climacool Running Shoes, #G59496, Grey/Turq/Org, Women's US Size 9.5Not Rated Womens Coza Open Toe Slide Flats, Nude, Size 8.0 NeHS , Highlighter orange Classic Saucony running shoesWomens Skechers Shape Ups Walking Shoes Sz 6.5 White SparkleBX466 SUSIMODA shoes brown patent leather suede women sneakersVans Runner Aqua Sea Blue Skate Shoes Size Men 6.5 Women 8 , *h2o REPEL* NIKE FREE XT MOTION FIT Women 6.5 trainer training running run trailwomen's easy spirit sneakers size 6 1/2 mediumAsics Patriot 9 Black/Carbon/White Sportstyle Running Trainers 2018 T873N-9097Reebok Easy Tone Womens 7.5 M Running Athletic Trainers Shoes White Blue WalkingReebok Easy Tone Fitness Athletic Toning Shoes Womens sz US 7 PURPLEBrooks GTS 17 Womens Size 10 D Athletic Running Wide Shoes Gray RedNike Zoom Rival S 8 Track Shoes Women's Sz 12 Running Spikes Blue 806558-401Nike Flex Trainer 5 Women's Training Shoe Size 7 TEAL/VOLT 724858 300 EUC ,
"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."