But when the question of how to explore the lake came up, not long after its discovery, the Vostok scientists faced a serious dilemma. The lake is under immense pressure, and to breach the ice would have devastating consequences.
Roger Federer: Swiss star will play on until at least 2019. Updated 1815 GMT (0215 HKT) February 21, 2017. Chat with us in Facebook Messenger. Find out what's happening in the world as it unfolds.
Roger Federer feels at home as one of the sport's greatest players to step onto a grass court. The Swiss, who is returning to tour-level play this week at the Mercedes Cup in Stuttgart, has won 15 tour-level titles on the surface, including seven at Wimbledon and eight in Halle.