Washington, Nov 8 : Scientists have found a crater made by the cosmic object that caused a massive explosion in the Siberian forest of Russia in 1908.

Known as the Tunguska event, it involved a fireball exploding 10 kilometers above the forests of Tunguska, flattening more than 800 square miles of the woodland. The blast also released 15 megatons of energy (about a thousand times that of the atomic bomb dropped on Hiroshima) and flattened 770 square miles (2,000 square kilometers) of forest.

Since then many teams of scientists have combed the site, but none was able to find any fragments of an object, like a rocky asteroid or a comet, that might have caused the event.

Now, the discovery of the crater under a lake near the Podkamennaya Tunguska River, wold be able to shed light on the cataclysm.

For the new study, a team of Italian scientists used acoustic imagery to investigate the bottom of Lake Cheko, about five miles (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," said Luca Gasperini, a geologist with the Marine Science Institute in Bologna. "We searched its bottom looking for extraterrestrial particles trapped in the mud. We mapped the basin and took samples," he added.

"When we examined the data, we couldn't believe what it was suggesting. The funnel-like shape of the basin and samples from its sedimentary deposits suggest that the lake fills an impact crater," said Gasperini .

This is further proved by the shape of the basin of Lake Cheko.

According to scientists, the basin is not circular, deep, and steep like a typical impact crater. Instead, it's elongated and shallow, about 1,640 feet (500 meters) long with a maximum depth of only 165 feet (50 meters). It also lacks the rim of debris usually found around typical impact craters, such as the Meteor Crater in Arizona.

The research team has said that the basin's unusual shape is the result of a fragment thrown from the Tunguska explosion that plowed into the ground, leaving a long, trenchlike depression.

"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 ( 0.6 mile a second)," said Gasperini. "It splashed on the soft, swampy soil and melted the underlying permafrost layer, releasing CO2 (carbon dioxide), water vapour, and methane that broadened the hole. Hence the shape and size of the basin, unusual for an impact crater," he added.

But scientists are not sure whether it was an asteroid or a comet responsible for the devastation

According to William Hartmann, a scientist at the Planetary Science Institute in Tucson, Arizona, "The new findings are compelling but do not address all of the lingering questions about the event."

"Finding fragments from the explosion is considered key to determining what kind of object made the impact. An asteroid would probably leave some remains, while a comet might be annihilated in the blast," said Hartmann. "If the body was an asteroid, a surviving fragment may be buried beneath the lake. If it was a comet, its chemical signature should be found in the deepest layers of sediments," he adds.

Gasperini and his colleagues are planning to go back to Siberia next year to search for more, and perhaps more conclusive, clues to the century-old puzzle. "We want to dig deeply in the bottom of the lake to definitively test our hypothesis and try to solve the Tunguska mystery," he stated. (ANI)