Tunguska Crater Mystery Solved?

Now, a team of Italian researchers claim to have found a clue that might help in unravelling the near century old mystery: The 164-foot-deep Lake Cheko, located just five miles northwest of the epicentre of the destruction.

"When we looked at the bottom of the lake, we measured seismic waves reflecting off of something. Nobody has found this before. We can only explain that and the shape of the lake as a low-velocity impact crater," said Giuseppe Longo, a physicist at the University of Bologna in Italy and co-author of the study.

During a 1999 expedition, Longo's team didn't plan to investigate Lake Cheko as an impact crater, but rather to look for meteoroid dust in its submerged sediments. While sonar-scanning the lake's topography, they were struck by its cone-like features.

Going a step further, Longo's team dove to the bottom and took six-foot core samples, revealing fresh mud-like sediment on top of "chaotic deposits" underneath.

"Expeditions in the 1960s concluded the lake was not an impact crater, but their technologies were limited. With the advent of better sonar and computer technologies, the lake took shape," he said.

However, as Longo said, samples were inconclusive of a meteorite impact.

"To really find out if this is an impact crater, we need a core sample 10 meters (33 feet) into the bottom in order to investigate a spot where the team detected a "reflecting" anomaly with their seismic instruments," he said.

Longo believes the lake could be where the ground was compacted by an impact or where part of the meteorite itself lay.

The object, if found, could be more than 30 feet in diameter and weigh almost 1,700 tons--the weight of about 42 fully-loaded semi-trailers.

Longo's team plans to return to Lake Cheko next summer, close to the 100th anniversary of the Tunguska Event.

"This is important work because we can make better conclusions about how cosmic bodies impact the Earth, and what they're made of, and it could help us find ways to protect our planet from future impacts of this kind," he said.

The findings are detailed in this month's online version of the journal Terra Nova.