By Paul Rincon
Scientists have identified a possible crater left by the biggest space impact in modern times - the Tunguska event.
The blast levelled more than 2,000 sq km of forest near the Tunguska River in Siberia on 30 June 1908.
A comet or asteroid is thought to have exploded in the Earth's atmosphere with a force equal to 1,000 Hiroshima bombs.
Now, a University of Bologna team says a lake near the epicentre of the blast may be occupying a crater hollowed out by a chunk of rock that hit the ground.
Lake Cheko - though shallow - fits the proportions of a small, bowl-shaped impact crater, say the Italy-based scientists.
Their investigation of the lake bottom's geology reveals a funnel-like shape not seen in neighbouring lakes.
In addition, a geophysics survey of the lake bed has turned up an unusual feature about 10m down which could either be compacted lake sediments or a buried fragment of space rock.
Other features suggest a recent origin for the lake.