The researchers are in a race against time to drill a borehole through the ice to retrieve samples of water and mud from Lake Ellsworth in West Antarctica which may harbour unique microbial life forms isolated from the rest of the biosphere from the time the ice cap first formed.
The 12-man team from the British Antarctic Survey in Cambridge had hoped to penetrate through the ice with a sterile hot-water drill to reach the lake today but technical difficulties are believed to have put the scientists behind schedule.
Lake Ellsworth is one of at least 387 lakes of liquid water formed at the base of the Antarctic ice sheet by the combined effects of geothermal heating and the high pressure of the huge volume of ice lying overhead.
At a depth of 60m (197ft), the scientists experienced technical problems with the sensors on the drill nozzle, which meant that the drilling had to be suspended. This followed an earlier problem with the main burner unit of the water boiler. However, the boilers have now successfully heated thousands of litres of snow to 90C for feeding the high-pressure water drill.
"We are now committed, having gone past the point of no return. If anything stops working now, water could freeze in the pipes and the whole programme could come to a halt," said Chris Hill, the expedition leader.
However, in the past few days, further technical problems have jeopardised the entire mission. In an email to The Independent they said: "Over the weekend a technical issue halted hot water drilling at Sub-glacial Lake Ellsworth. It is too early at this stage to say what this may mean for the project. The engineering team is currently investigating the cause and will keep us informed of developments."
Once the main borehole, which is just 40cm wide, has broken through to the surface of the sub-glacial lake, the scientists have about 24 hours to retrieve their samples before the borehole freezes over and becomes unusable.
The first probe will collect water samples at different depths of the lake. A second probe will be lowered to penetrate the soft sediments on the lake bed, which will provide critical data on the history of the West Antarctic ice sheet and the past climate of the Earth.
The drilling equipment and instruments have been sterilised to eliminate the risk of microbial contamination. The water used for drilling has also been filtered and treated with ultraviolet light, as well as being heated to 90C, to prevent surface contaminants reaching the lake.
Martin Siegert, from the University of Bristol, principal investigator, said: "We are about to explore the unknown and I am very excited that our mission will advance our scientific understanding of Antarctica's hidden world."