(meteorobs) Southern Arizona Fireball - Jun 23

[Skywayinc at aol.com]

A most interesting news release about  a  
long-standing cosmic mystery. -- joe rao



June 24, 2009
 
Media Contact:
Blaine Friedlander
Cornell  Press Relations Office
1 (607) 254-8093
_bpf2 at cornell.edu_ (mailto:bpf2 at cornell.edu)  
 
BACK TO THE FUTURE: SPACE SHUTTLE SHOWS  HOW
1908 TUNGUSKA EXPLOSION WAS CAUSED BY A COMET
 
The mysterious 1908 Tunguska explosion that leveled 830  square miles
of Siberian forest was almost certainly caused by a comet  entering the
Earth’s atmosphere, says new Cornell University research.  The
conclusion is supported by an unlikely source: the exhaust plume  from
the NASA space shuttle launched a century later.
 
The research, accepted for publication (June 24, 2009)  by the journal
Geophysical Research Letters, published by the American  Geophysical
Union, connects the two events by what followed each about a  day
later: brilliant, night-visible clouds, or noctilucent clouds,  that
are made up of ice particles and only form at very high altitudes  and
in extremely cold temperatures.
 
“It’s almost like putting together a 100-year-old murder  mystery,”
said Michael Kelley, the James A. Friend Family  Distinguished
Professor of Engineering at Cornell, who led the research team.  “The
evidence is pretty strong that the Earth was hit by a comet in  1908.”
Previous speculation had ranged from comets to meteors.
 
The researchers contend that the massive amount of water  vapor spewed
into the atmosphere by the comet’s icy nucleus was caught up  in
swirling eddies with tremendous energy by a process  called
two-dimensional turbulence, which explains why the noctilucent  clouds
formed a day later many thousands of miles away.
 
Noctilucent clouds are the Earth’s highest clouds,  forming naturally
in the mesosphere at about 55 miles over the polar regions  during the
summer months when the mesosphere is around minus 180  degrees
Fahrenheit (minus 117 degrees Celsius). The space shuttle  exhaust
plume, the researchers say, resembled the comet’s action. A  single
space shuttle flight injects 300 metric tons of water vapor into  the
Earth’s thermosphere, and the water particles have been found  to
travel to the Arctic and Antarctic regions, where they form the  clouds
after settling into the mesosphere.
 
Kelley and collaborators saw the noctilucent cloud  phenomenon days
after the space shuttle Endeavour (STS-118) launched on Aug.  8, 2007.
Similar cloud formations had been observed following launches in  1997
and 2003.
 
Following the 1908 explosion, known as the Tunguska  Event, the night
skies shone brightly for several days across Europe,  particularly
Great Britain -- more than 3,000 miles away. Kelley said he  became
intrigued by the historical eyewitness accounts of the aftermath,  and
concluded that the bright skies must have been the result  of
noctilucent clouds. The comet would have started to break up at  about
the same altitude as the release of the exhaust plume from the  space
shuttle following launch. In both cases, water vapor was injected  into
the atmosphere.
 
The scientists have attempted to answer how this water  vapor traveled
so far without scattering and diffusing, as conventional  physics would
predict.
 
“There is a mean transport of this material for tens of  thousands of
kilometers in a very short time, and there is no model that  predicts
that,” Kelley said. “It’s totally new and unexpected  physics.”
 
This “new” physics, the researchers contend, is tied up  in
counter-rotating eddies with extreme energy. Once the water vapor  got
caught up in these eddies, the water traveled very quickly -- close  to
300 feet per second.
 
Scientists have long tried to study the wind structure  in these upper
regions of the atmosphere, which is difficult to do by  such
traditional means as sounding rockets, balloon launches  and
satellites, explained Charlie Seyler, Cornell professor of  electrical
engineering and paper co-author.
 
“Our observations show that current understanding of  the
mesosphere-lower thermosphere region is quite poor,” Seyler said.  The
thermosphere is the layer of the atmosphere above the  mesosphere.
 
                                # # #
 
The paper is also co-authored by physicist Miguel  Larsen, Ph.D. ‘79,
of Clemson University, and former student of Kelley. The  work
performed at Cornell was funded by the Atmospheric Science Section  of
the National Science Foundation.
 
On July 1, Kelley will give a lecture, “Two-dimensional  Turbulence,
Space Shuttle Plume Transport in the Thermosphere, and a  Possible
Relation to the Great Siberian Impact Event,” at a plenary session  of
the annual meeting of Coupling, Energetics and Dynamics of  Atmospheric
Regions in Sante Fe, N.M.
 
The paper is available at:
_http://www.agu.org/journals/gl/papersinpress.shtml_ 
(http://www.agu.org/journals/gl/papersinpress.shtml)  
 
(Text by Anne Ju, Cornell  Chronicle)

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