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.
Federer, fresher at 35, will seek his record eighth Wimbledon title against Marin Cilic, who beat Federer en route to winning the 2014 U.S. Open and wound up falling despite three match points against Federer in a 2016 Wimbledon quarterfinal.