 |
| Crater Could Solve 1908 " Tunguska Meteor " Mystery |
Astronomers
have been left to guess whether the object was an asteroid or a comet, and figuring
out what it was would allow better modeling of potential future calamities.
Italian
researchers now think they've found a smoking gun: The 164-foot-deep Lake
Cheko, located just 5 miles northwest of the epicenter of destruction.
"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."
Should the team turn up conclusive
evidence of an asteroid or comet on a later expedition, when they obtain a
deeper core sample beneath the lake, the remaining mysteries surrounding the
Tunguska event may be solved.
The findings are detailed in this month's online version of the journal Terra Nova.
 |
| Crater Could Solve 1908 " Tunguska Meteor " Mystery |
Submerged evidence
During a 1999 expedition, Longo's team
didn't plan to investigate Lake Cheko as an impact crater, but rather to look
for meteoroid dust in its submerged sediments. While sonar-scanning the lake's
topography, they were struck by its cone-like features.
"Expeditions in the 1960s concluded
the lake was not an impact crater, but their technologies were limited,"
Longo said. With the advent of better sonar and computer technologies, he
explained, the lake took shape.
Going a step further, Longo's team dove to
the bottom and took 6-foot core samples, revealing fresh mud-like sediment on
top of "chaotic deposits" beneath. Still, Longo explained the samples
are inconclusive of a meteorite impact.
"To really find out if this is an
impact crater," Longo said, "we need a core sample 10 meters (33
feet) into the bottom" in order to investigate a spot where the team
detected a "reflecting" anomaly with their seismic instruments. They
think this could be where the ground was compacted by an impact or where part
of the meteorite itself lies: The object, if found, could be more than 30 feet
in diameter and weigh almost 1,700 tons — the weight of about 42 fully-loaded
semi-trailers.
 |
| Crater Could Solve 1908 " Tunguska Meteor " Mystery |
Caution for now
From a UFO crash to a wandering
black hole, wild (and wildly unsupported) explanations for the Tunguska event
have been proposed. Alan Harris, a planetary scientist at the Space Science
Institute in Boulder, Colorado, said the proposal by Longo's team isn't one of
them.
"I was impressed by their work and I
don't think it's something you can wave off," said Harris, who was not
involved in the research.
Longo and his team "are among the
recognized authorities on Tunguska" in the world, Harris told SPACE.com.
"It would be thrilling to dig up chunks of the meteor body if they can
manage to. It would lay the question to rest whether or not Tunguska was a
comet or asteroid."
Some researchers, however, are less
confident in the team's conclusions.
"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. That only a fragment
of the main explosion reached the ground and made a relatively small crater,
without creating a larger main crater, seems contradictory to Morrison.
Harris agreed that physics could work against Longo's explanation, but did note that similar events — with impact craters — have been documented all over the world.
"In 1947, the Russian Sikhote-Alin
meteorite created 100 small craters. Some were 20 meters (66 feet)
across," Harris said. 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 (Longo's
team) will unearth some meteorite material," Harris said.
Longo's team plans to return to Lake Cheko
next summer, close to the 100th anniversary of the Tunguska Event. "This
is important work because we can make better conclusions about how cosmic
bodies impact the Earth, and what they're made of," Longo said. "And
it could help us find ways to protect our planet from future impacts of this
kind."
Would your
friends be interested? Share this story!
By Dave Mosher
( Keywords )
BULLSHIT
ردحذفإرسال تعليق