By Bob McDonald, Quirks & Quarks

A Russian drilling expedition in Antarctica is close to breaking through four kilometres of ice to sample the pristine waters of Lake Vostok, which has not seen daylight for millions of  years. 

It's a fascinating project, but it has international scientists seriously concerned about contamination of a lake that might have been isolated from the rest of world for tens of millions of years. 

A sub-glacial lake, about the size and shape of Lake Ontario, Lake Vostok is one of the largest fresh water lakes in the world, yet it remained unknown until the 1990s. 

Since then, satellite data and radar measurements have revealed that Vostok is just one of several lakes hidden under the Antarctic ice cap. A combination of pressure from the ice above and heat from the Earth below keeps these lakes liquid even though they are located in the coldest region of the planet.

Scientists are anxious to sample the waters of the lakes to look for microbes that could be unlike any others on Earth since they live in isolated environments virtually cut off from all other life on the planet.

If life has persisted down there, it raises hopes that similar life could exist in oceans under the icy surfaces of frozen moons of Jupiter and Saturn.

Photos of Jupiter's moon Europa show a surface totally covered in ice, with fracture patterns indicating that the ice moves around and must therefore be floating on a global ocean.

Saturn's icy moon Enceladus is actually spewing water out of ice volcanoes erupting at it's south pole. These moons could hold our first proof that life exists beyond Earth.

But drilling through kilometres of ice on a distant frozen moon is an enormously difficult and expensive task that is not likely to happen for decades, which is why the Antarctic expedition is so compelling. 

The biggest challenge in reaching Lake Vostok, however, is investigating this pristine environment without contaminating or changing it.

The drilling technology used by the Russians involves hot water and drilling fluids such as kerosene, which are substances that ideally you do not want to enter Lake Vostok.

The scientists must also make sure that the drill bit and any instruments inserted into the water do not contain any microbes from the surface. That would not only mess up the scientific readings, but could expose the microbes in the lake to what amounts to an invasive species.

Another Antarctic drilling project into sub-glacial Lake Ellesworth by a British team is using more modern equipment and taking extreme precautions to make sure their equipment is sterilized.

Neither project has broken through yet. 

One suggestion to protect the lake water is to allow it to flow up into the drill hole and take samples from there. 

But in fact, the most valuable information about life and the history of the lake lies in the mud and sediments at the bottom, which means eventually, sending a probe down through the entire water column.

This isn't the first time science has been in a position to learn a tremendous amount about a new environment but at the same time, risked contaminating exactly what was being studied.  Just look at the tons of equipment left scattered all over the moon. 

At least the robotic landers sent to Mars are baked before leaving Earth to get rid of microbes.

There is the possibility that the life in Lake Vostok is not so isolated or as old as previously thought. Radar data suggests the lakes may occasionally become connected so there would be a flow between them. The ice above is also moving, which could transport microbes out of the lakes.

Whatever the case, scientists involved in Antarctic research are watching the drilling projects closely to ensure every precaution is taken to preserve the purity of the sub-glacial lake environment.

If new forms of life are found down there and the water is contaminated, that life will have to deal with what to them would be an alien invasion by humans.