Here's some bad news for anyone still hoping life exists on Mars: Antarctic permafrost similar to permafrost on Mars seems to be too cold and dry to support microbes.
Canadian and U.S. researchers were unable to find any micro-organisms that were living or breeding in the permafrost of a dry, high-elevation valley in the Antarctic, they reported this week in the ISME Journal.
"It doesn't mean there's no life on Mars, but what it does mean is it's going to be harder to find," said Jacqueline Goordial, the McGill University researcher who led the study, in an interview with Rachelle Solomon on CBC's Breakaway.
Her doctoral research supervisor, Prof. Lyle White, had an even more pessimistic analysis of the situation.
"If conditions are too cold and dry to support active microbial life on an analogous climate on Earth, then the colder dryer conditions in the near surface permafrost on Mars are unlikely to contain life," he said in a statement. "Additionally, if we cannot detect activity on Earth, in an environment which is teeming with micro-organisms, it will be extremely unlikely and difficult to detect such activity on Mars."
Because water is needed to support life as we know it, the hunt for life on Mars — a planet that is now cold and dry all over — relies on "following the water." Much of the water that remains on the Red Planet is thought to be in the form of underground permafrost similar to the permafrost found in Antarctica's high-elevation McMurdo Dry Valleys.
University Valley is one of them. It's 1,700 metres above sea level and extremely cold — it has an average temperature of –23 C and never gets above 0 C. The McMurdo Dry Valleys are also the second-driest place on Earth, after the Atacama Desert in Chile.
Goordial, who did the study while she was a Ph.D. student working with Whyte, had high hopes for University Valley.
"We thought we would find some of the most cold-adapted and toughest organisms out there," she said.
She was part of a scientific expedition to University Valley affiliated with NASA's ASTEP program (astrobiology science and technology for exploring planets) in 2013. Braving "summer" temperatures between –15 C and –20 C, she worked all day and slept in a tent at night for two weeks.
Like 'sand at the beach'
The McMurdo dry valleys contain a double-layered permafrost that is found nowhere else on Earth, but is common in the northern polar regions of Mars studied by NASA's Phoenix lander for five months starting November 2008.
The area contains some of the "oldest, driest and coldest soils that we have on Earth," Goordial said.
The upper layer of the permafrost in University Valley is less than 3 per cent water.
"It just looks like sand at the beach," Goordial recalled. Underneath that is "ice-cemented" permafrost, containing higher levels of ice that formed when scant water vapour in the air was deposited as frost over hundreds of thousands of years.
A major goal of the expedition was to test a drill designed to drill through permafrost on Mars.
Researchers removed cylinders of permafrost between 42 and 55 centimetres deep that they could search through.
"Drilling in permafrost is quite hard," Goordial recalled. The drill generates heat that melts the ice, and if the drill was stopped at any point by an obstacle such as a rock, the melted ice would refreeze, trapping the drill in the ground. "And that's a huge pain."
When Goordial analyzed the permafrost samples, she didn't find the hardy living, microbes she was expecting — in any layer.
"Instead, they were either dormant or dead," she said.
She suspects the dead microbes were a combination of those blown in by the wind from other places and those that have fallen down from the warmer, wetter valley walls.
She added, "I myself was quite surprised at these results and repeated some of the experiments several times because I didn't believe them."
Thriving microbial communities have previously been found in seemingly unlikely places all over the Earth, from the deep sea to several kilometres underground, as well as in permafrost in other extremely cold reaches of the Arctic and Antarctic.
"Previous studies in the lower dry valleys of Antarctica and in subglacial lakes were giving us the impression that microbial life was rich in the cold regions," said Chris McKay, a researcher at NASA's Ames Research Centre who co-authored the paper, in a statement. But he noted that University Valley is more like Mars than any of those places.
"This is certainly the training ground for the search for evidence of life on Mars and an extremely important result for NASA's astrobiology effort."
Alberto Fairen, a NASA Astrobiology Institute associate with the Centro de Astrobiologica in Madrid, Spain, and a visiting scientist Cornell University, was also surprised.
"We have been investigating the limits of life on Earth for decades, including extremes of pH, salinity or temperature, and so far we found life everywhere we searched for," he said in an email. "This is the first actual limit we can put to life distribution on our planet, and it is very significant that the limit is found when environmental conditions are very similar to those on Mars' surface."
In a way, that's good news, he said — it means that microbes from Earth probably can't contaminate Mars, as some researchers fear.
It also doesn't necessarily mean there isn't life on Mars — just that it's different from life on Earth, he suggests, "as potential Martian micro-organisms would have had a totally different evolutionary story and billions of years to adapt to the extremes in a changing environment."