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Mystery Space Blast 'Solved'

From: UFO UpDates - Toronto <ufoupdates@home.com>
Date: Fri, 02 Nov 2001 09:13:02 -0500
Fwd Date: Fri, 02 Nov 2001 09:13:02 -0500
Subject: Mystery Space Blast 'Solved'


Tuesday, 30 October, 2001, 18:13 GMT

Mystery Space Blast 'Solved'

By BBC News Online science editor
Dr David Whitehouse

Astronomers may have solved the puzzle of what it was that
brought so much devastation to a remote region of Siberia almost
a century ago.

In the early morning of 30 June, 1908, witnesses told of a
gigantic explosion and blinding flash. Thousands of square
kilometres of trees were burned and flattened.

Scientists have always suspected that an incoming comet or
asteroid lay behind the event - but no impact crater was ever
discovered and no expedition to the area has ever found any
large fragments of an extraterrestrial object.

Now, a team of Italian researchers believe they may have the
definitive answer. After combining never-before translated
eyewitness accounts with seismic data and a new survey of the
impact zone, the scientists say the evidence points strongly to
the object being a low-density asteroid.

They even think they know from where in the sky the object came.

Completely disintegrated

"We now have a good picture of what happened," Dr Luigi
Foschini, one of the expedition's leaders, told BBC News Online.

The explosion, equivalent to 10-15 million tonnes of TNT,
occurred over the Siberian forest, near a place known as

Only a few hunters and trappers lived in the sparsely populated
region, so it is likely that nobody was killed. Had the impact
occurred over a European capital, hundreds of thousands would
have perished.

A flash fire burned thousands of trees near the impact site. An
atmospheric shock wave circled the Earth twice. And, for two
days afterwards, there was so much fine dust in the atmosphere
that newspapers could be read at night by scattered light in the
streets of London, 10,000 km (6,213 miles) away.

But nobody was dispatched to see what had happened as the Czars
had little interest in what befell the backward Tungus people in
remote central Siberia.

Soil samples

The first expedition to reach the site arrived in 1930, led by
Soviet geologist L A Kulik, who was amazed at the scale of the
devastation and the absence of any impact crater. Whatever the
object was that came from space, it had blown up in the
atmosphere and completely disintegrated.

Nearly a century later, scientists are still debating what
happened at that remote spot. Was it a comet or an asteroid?
Some have even speculated that it was a mini-black hole, though
there is no evidence of it emerging from the other side of the
Earth, as it would have done.

What is more, none of the samples of soil, wood or water
recovered from the impact zone have been able to cast any light
on what the Tunguska object actually was.

Researchers from several Italian universities have visited
Tunguska many times in the past few years. Now, in a pulling
together of their data and information from several hitherto
unused sources, the scientists offer an explanation about what
happened in 1908.

Possible orbits

They analysed seismic records from several Siberian monitoring
stations, which combined with data on the directions of
flattened trees gives information about the object's trajectory.
So far, over 60,000 fallen trees have been surveyed to determine
the site of the blast wave.

"We performed a detailed analysis of all the available
scientific literature, including unpublished eye-witness
accounts that have never been translated from the Russian," said
Dr Foschini. "This allowed us to calculate the orbit of the
cosmic body that crashed."

The object appears to have approached Tunguska from the
southeast at about 11 km per second (7 miles a second). Using
this data, the researchers were able to plot a series of
possible orbits for the object.

Of the 886 valid orbits that they calculated, over 80% of them
were asteroid orbits with only a minority being orbits that are
associated with comets. But if it was an asteroid why did it
break up completely?

"Possibly because the object was like asteroid Mathilde, which
was photographed by the passing Near-Shoemaker spaceprobe in
1997. Mathilde is a rubble pile with a density very close to
that of water. This would mean it could explode and fragment in
the atmosphere with only the shock wave reaching the ground."

The research will be published in a forthcoming edition of the
journal Astronomy and Astrophysics.

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