Team makes Tunguska crater claim

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.Luca Gasparini, Giuseppe Longo and colleagues from Bologna argue that the lake feature, about 8km north-north-west of the airburst epicentre, may have been gouged out by remnant material that made it to the ground. "We have no positive proof this is an impact crater, but we were able to exclude some other hypotheses, and this led us to our conclusion," Professor Longo, the research team leader, told BBC News.