The Mystery of Tunguska

Ninety-nine years ago this weekend, something remarkable and violent happened over the the forests of Siberia. Something–perhaps a comet or meteorite–came tearing into the atmosphere and probably exploded in midair with a force a thousand times greater than that of the bomb used at Hiroshima.  It leveled more than 800 square miles of trees.  It has come to be known as the Tunguska Event.  The date was June 30, 1908, and the sky lit up across Asia and Europe.  What was it?  The trail runs cold.  No impact crater was ever found, no proof of what actually caused the blast. But now a team of Italian scientists reports it has looked at a small oval lake, about five miles northwest of the center of the blast, and believes it could be the long-mysterious impact crater.  It’s called Lake Cheko.  They report their finding in an online British journal called Terra Nova, which can be found HERE. "Its funnel-like bottom morphology and the structure of its sedimentary deposits, revealed by acoustic imagery and direct sampling, all suggest that the lake fills an impact crater," write Luca Gasperini and his colleagues.  Gasperini is a geologist at the University of Bologna.  To make their point, his team has made a computer illustration (above) of what the lake would look like if the water in it were 40 meters (about 130 feet) lower.  The lake is actually only about 165 feet deep.  Many craters on the moon are shallow.  But they also have elevated rims, believed to have been caused by material ejected from the crater when it formed.  In the case of Lake Cheko, Gasperini et al suggest the rim may have collapsed over time; the area is marshy in summer. What’s more, there’s this curiosity: Lake Cheko does not appear on any maps of the region before 1929, though the researchers concede that Tunguska is so remote it was not thoroughly mapped before then. There’s an old line in science that "extraordinary claims demand extraordinary proof," and there’s a lot of skepticism among scientists who’ve heard about the paper. "I will be very pleasantly surprised if there turns out to be anything to this at all," said Stephen Maran, a veteran NASA astronomer, now retired, who is the author of "Astronomy for Dummies" and other works.  "It’s not outrageous; the real question is whether this lake is so unusual as to demand a special theory of origin." Sky and Telescope (a hat tip to David Tytell there) caught wind of the paper and located Lake Cheko on Google Maps.  Take a look HERE.  If it was ever round or elliptical, it’s changed now. Extraordinary claims do demand extraordinary proof.  We’re talking about something extraordinary that happened, in a very remote place, a century ago. (Image from University of Bologna, via Blackwell Synergy, publishers of Terra Nova.)