Antarctica started to ice over about 30 million years ago. Technically speaking, the entire continent is a desert with an average of two inches of rain per year. It is the coldest, windy-est and most difficult of places to work on the planet.
The difficulty in drilling to these depths on the ice is first the ice is not static, its moving. Secondly that the drill hole will collapse over time so you may have to re-drill sections of the bore hole.
Drilling down to Lake Vostok has always carried some controversy. Everyone agrees that the lake itself has not seen the outer world for millions of years so what life may exist there has taken an evolutionary path that will be unique and until now unseen. You want to sample that life but without potential contamination from the surface.
The core hole was filled with diesel fuel and kerosene to keep the ice from closing during the winter season but both of these however contain bacteria that will contaminate any sample brought up from the lake itself and potentially contaminate the lake itself.
The Russian team held off the last 300' of drilling until some of these concerns could be mitigated. Then someone calculated the internal pressure of the lake itself with two miles of ice sitting atop it!
They decided to take a decidedly 'surgical' approach to penetrating the lake. They switched from their diesel/kerosene solution to freon. That would limit any contamination they may introduce. Then then switched from the large diameter drill to a thermally heated drill probe just a few inches across.
Their plan was to push through into the lake, let the internal pressure equalize pushing up lake water into the drill hole, withdraw the drill probe and let the lake water freeze in the drill hole like a plug.
Using this approach they hopefully pushed any potential contaminates up the drill hole.
They will take samples from the frozen material in the drill hole next season and we'll see what came up in the wash.
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