Date: Thu Jun 25 2009 - 01:42:32 UTC

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    Perhaps a little off-topic, but
    a most  interesting news release about a 
    long-standing cosmic mystery and how it  might have finally 
    been solved by the Space Shuttle. -- joe  rao
    June 24, 2009
    Media Contact:
    Blaine  Friedlander
    Cornell Press Relations Office
    1 (607)  254-8093 
    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
    “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: 
    (Text by Anne  Ju, Cornell Chronicle)  
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