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Lake Cheko in the Siberian region of Tunguska has recently emerged as a candidate for an “impact site”
linked to the famous Tunguska explosion of 1908. Credit: www-th.bo.infn.it/tunguska / University of Bologna
 

Jul 05, 2007
New Tunguska Crater Found?

A team of Italian scientists has announced seismic evidence of what could be meteor fragments beneath Lake Cheko in Siberia--the first "solid evidence" of a Tunguska asteroid.

On June 30, 1908, a massive explosion detonated in the skies over Tunguska in northern Siberia. The resulting shock wave flattened some 60 million trees across 2000 square kilometers. The blast was heard hundreds of miles away and the cloud of dust colored the skies of the Northern Hemisphere for months afterwards.

The first expedition to investigate the region could not locate any sign of an impact event, nor did it recover any meteoric fragments. A later expedition, however, did uncover magnetite globules and various forms of silicate globules embedded in the earth and in the trees.

Most scientists eventually settled on either an icy comet explosively vaporized before reaching the surface, or a small rocky asteroid exploding in the atmosphere and leaving no appreciable fragments. But the absence of definitive evidence for an impact invited many exotic theories--ranging from “mirror-matter” or a tiny “quantum black hole,” to an exploding alien craft or a Nikola Tesla experiment gone awry.

In past discussions of the Tunguska event, our Picture of the Day editors have suggested electric discharge between a small comet or asteroid and the Earth. That suggestion was based on a wide variety of recorded physical effects and the testimony of human witnesses.

More recently, however, a team of Italian researchers has suggested that the 164-foot deep Lake Cheko, five miles northwest of the epicenter of the blast, could be the site of an impact by a meteor or a fragment of the body responsible for the devastating Tunguska event.

The team reported that 3D sonar images of the lake’s bottom indicate that it is funnel-shaped, something that might be expected of both an impactor and an electric discharge. Using seismic detectors, the University of Bologna scientists discovered an area of greater density beneath the lake, noting that this could indicate the remains of a meteor. "When we looked at the bottom of the lake, we measured seismic waves reflecting off of something," said Giuseppe Longo, a physicist at the University of Bologna in Italy and co-author of the study. "Nobody has found this before. We can only explain that and the shape of the lake as a low-velocity impact crater."

According to a report on the Space.com web site, however, some physicists are skeptical about the small size of the Lake Cheko crater. "We know from the entry physics that the largest and most energetic objects penetrate deepest," said David Morrison, an astronomer with NASA's Ames Research Center. Morrison wondered aloud why only a fragment of the main explosion would reach the ground to make a relatively small crater, while the greater portion would not create a larger main crater.

But Alan Harris, a planetary scientist at the Space Science Institute, points out that, in 1947, the Russian Sikhote-Alin meteorite created 100 small craters. Some were 20 meters (66 feet) across. A site in Poland also exists, he explained, where a large meteor exploded and created a series of small lakes. "If the fragment was traveling slowly enough, there's actually a good chance [the Italian team) will unearth some meteorite material," Harris said.

The researchers will return to Tunguska this summer with plans to drill beneath the bottom of Lake Cheko, hoping to find a meteorite. From an Electric Universe perspective, if the Tunguska explosion was the result of an electric discharge, a meteor fragment may indeed be found, pointing to the source of the discharge. But more likely, the increased density beneath the lake could be the signature of the electric arc that excavated the depression, producing the fused sands and soils of a fulgurite.

By Stephen Smith
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