|
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. Source : BBC News Online - Science
Shocking rocks 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. The object that hurtled through the atmosphere on the morning of 30 June, 1908, is thought to have detonated some 5-10km above the ground with an energy equivalent to about 20 million tonnes of TNT. The explosion was so bright it even lit up the sky in London, UK. Small fragments of the body should have survived the airburst and made it Earth. But, mysteriously, no crater - or even the slightest trace of the impactor - has ever been positively identified.  | " The impact cratering community does not accept structures as craters unless there is evidence of high temperatures and high pressures." Gareth Collins, Imperial College London | "In my opinion, they certainly haven't provided any conclusive evidence it's an impact structure," commented Dr Gareth Collins, a Natural Environment Research Council (Nerc) research fellow at Imperial College London, UK. He added: "The impact cratering community does not accept structures as craters unless there is evidence of high temperatures and high pressures. That requires evidence of rocks that have been melted or rocks that have been ground up by the impact." Finish reading the Article on the BBC News Site |
