The head of Russia’s mission to drill into an Antarctic lake sealed off from the world for 15 million years says it is too soon to say if his team has succeeded.

Media reports yesterday – citing an unnamed source originally quoted by Russian newswire RIA Novosti – said the project had finally reached the lake by drilling through the roughly 3,750 metres of ice that sit atop it.

But Valery Lukin, director of the Russian Antarctic programme, told Nature this morning that data from a number of sensors monitoring the drilling were still being analysed.

“Only when I have this can I say we penetrated [the lake],” he said. “We want to be sure we have really reached the surface of Lake Vostok.”

Information on the exact depth of ice drilled and the levels of various fluids in the borehole need to be carefully checked before the team can confirm that it has penetrated the lake, he added. The data might be processed by as soon as tomorrow.

“As soon as we get it officially confirmed, this information will be disseminated among the international community,” says Lukin.

The majority of the drilling team have now left Vostok Station, initially by air before transferring to the Russian icebreaker Akademik Fyodorov yesterday night. Only two members of the team have remained behind to monitor the borehole.

In December, a full complement of researchers will return and, assuming that Lake Vostok has finally been reached after two decades of work, the real science will begin.

For more on this project see our story Race against time for raiders of the lost lake from last year.