A team of Italian researchers working in a remote part of Siberia think that they may have found a crater caused by one of the largest asteroid impacts in modern-day history, known as the Tunguska event.

On the morning of 30 June 1908, a comet or asteroid exploded as it entered the Earth’s atmosphere, causing the sky over Siberia to light up. The explosion had a force equivalent to 1,000 times that of the atomic bomb dropped on Hiroshima and was visible from as far away as London.

Although the explosion levelled more than 2,000 square kilometres of taiga (coniferous forest, above) near Siberia’s Tunguska River, no trace of the impact or impactor has ever been found – until now.

The team of geophysicists from the University of Bologna said that Lake Cheko, which is located at the epicentre of the blast, may be occupying the impact crater and hiding a fragment of extraterrestrial rock, which would offer unequivocal evidence of the blast. The researchers discovered that unlike the neighbouring lakes, Cheko’s bed has a distinctive funnel shape (right), which corresponds to their simulations of low-velocity impacts. They also found
an unusual feature that could either be compacted lake sediments or remnants of an asteroid or meteor.

However, the findings are being contested by other researchers. ‘The impact cratering community does not accept structures unless there is evidence of high temperatures and high pressures,’ said Dr Gareth Collins, Natural Environment Research Council research fellow at Imperial College, London.

The team is planning to return to the region next summer to drill under the lake’s bed and take core samples in order to determine whether or not the underlying rock is extraterrestrial in origin.

September 2007