Saturday, November 17, 2007

Tunguska crater found at last

The misterious explosion that occured nearly 100 years ago in Russia, known as Tunguska event is once again in the headlines.

This cataclysm puzzled scientists for the last 100 years, since it was first studied. On June 30,1998, scientists believe a ball of fire exploded 10Km above ground in the Siberian forest. The blast was a thousand times more powerful than the atomic bomb dropped in Hiroshima, flattening 60 million trees in an area of 2.000 square kilometers.

Although they suspected a comet or a meteor to have caused this, no fragments were ever found to support this theory... until now.

(see map).

A team of Italian scientists has now used acoustic imagery to investigate the bottom of Lake Cheko, about eight kilometers north of the explosion's suspected epicenter.

"When our expedition [was at] Tunguska, we didn't have a clue that Lake Cheko might fill a crater,"

"We searched its bottom looking for extraterrestrial particles trapped in the mud. We mapped the basin and took samples. As we examined the data, we couldn't believe what they were suggesting.

"The funnel-like shape of the basin and samples from its sedimentary deposits suggest that the lake fills an impact crater,"

This was never noticed before because, unlike traditional impact craters with it circular deep basins and steep walls, Lake Cheko has an elongated and shallow crater.

"We suggest that a 10-meter-wide [33-foot-wide] fragment of the object escaped the explosion and kept going in the same direction. It was relatively slow, about 1 kilometer a second".

"It splashed on the soft, swampy soil and melted the underlying permafrost layer, releasing CO2, water vapor, and methane that broadened the hole, hence the shape and size of the basin, unusual for an impact crater. Our hypothesis is the only one that accounts for the funnel-like morphology of Lake Cheko's bottom,"

However, some specialists still have their doubts - William Hartmann, senior scientist of the Planetary Science Institute in Tucson, Arizona puts it:

"It's an exciting result that might shed new light on the Tunguska explosion,"

"But it raises a question in my mind: If one large fragment hit the ground, we would normally expect thousands of smaller fragments also to hit the ground along the path, and many searches have failed to find such meteorite fragments. So, why no smaller pieces?"

A new trip to Siberia is being planned by Gasperini and his colleagues to try and solve this ancient puzzle once and for all:

"We want to dig deeply in the bottom of the lake to definitively test our hypothesis and try to solve the Tunguska mystery,"

Source [National Geographic]

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