An enormous lake that has lain buried under Antarctic ice for millions of years is home to a new kind of bacterial life, Russian scientists claim.
The researchers found evidence for the unidentified organism in water samples brought up from Lake Vostok, the largest subglacial lake on the Antarctic continent.
The Russian team found seven samples of the mystery species in water that had frozen on a drill head used to reach the lake that lies beneath an ice sheet more than two miles (3.5km) thick.
The scientists extracted strands of DNA from the organism, but said the genetic code was never more than an 86% match with any of the species listed in global databanks. Sergey Bulat, a researcher on the team at the Petersburg Nuclear Physics Institute, said that anything less than a 90% match usually indicated that the organism was unknown.
"We call it unidentified and 'unclassified' life," Bulat told the state news agency, RIA Novosti. "If it were found on Mars, people would call it Martian DNA. But this is DNA from Earth," he added.
The Russian team broke through to the lake under the East Antarctic Ice Sheet last year. When the ice cover was pierced, water burst up through the borehole. The huge body of water stretches for 150 miles and is 30 miles wide in places.
Several expeditions have set out to look for life in Antarctica's subglacial lakes. The organisms are likely to be different from well-known life because they have evolved in isolation, under intense pressure, and with no sunlight, for millions of years.
"It's rather tantalising," said David Pearce, a microbiologist at the British Antarctic Survey. "We can't read too much into it yet, but I would be surprised and disappointed if they had not found anything. This whets the appetite for what is to come."
The Russian team said it planned more tests, but needed more specimens of the bugs. Those might be among water samples collected from the lake earlier this year, which are being carried by ship back to the Russian mainland.
The scientists ultimately hope to grow the bacteria so they can study their size, shape and physiology, and confirm whether or not the bugs are new to science.
In January this year, a US team broke through 800 metres of Antarctic ice to reach Lake Whillans, another subglacial lake. Water samples brought up from the lake also contained microbial life.
On Christmas Day last year, a British team aborted an expedition to drill through almost two miles of ice to Lake Ellsworth in Antarctica after failing to link two boreholes to recirculate drilling water back to the surface.