
The scars on the landscape can still be seen today
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.
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The asteroid was probably a pile of space rubble - like Mathilde
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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.
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The direction of the flattened trees is a vital clue
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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.
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Over 60,000 fallen trees have been surveyed to determine the site of the blast wave
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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.
source : BBC News
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