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(meteorobs) Fwd: Meteor High-Speed Imaging [Leonid MAC]
------- Forwarded Message
From: Ron Baalke <baalke@zagami.jpl.nasadot gov>
Subject: Meteor High-Speed Imaging
Date: Tue, 18 Dec 2001 08:30:52 -0800 (PST)
http://leonid.arc.nasadot gov/recent_updates6.html
METEOR HIGH-SPEED IMAGING
Leonid Multi-Instrument Aircraft Campaign (MAC)
Ames Research Center
December 11, 2001
High speed imaging has now for the first time shown details in the head
of a meteor that reveil the dimensions and shape of the sources of light
that make a shooting star. In a series of unique images obtained by
Leonid MAC participant Prof. Hans Stenbaek-Nielsen of the University
of Alaska, a meteor is seen to develop from a ball of light into a an
object with a bow shock and a tail. These results were unveiled in a
standing-room only special session "The 2001/2002 Leonid meteor storms"
at the Fall Meeting of the American Geophysical Union in San Francisco
on December 11, 2001.
Prof. Nielsen used an unusual intensified high frame-rate camera,
specially designed for sprite observations. This camera records video
images at a rate of 1000 frames per second. Nielsen, a Danish national,
observed from a site at Pokers Flat, Alaska, and had to continually
watch a video screen to catch the meteor in flight. The images shown
above are frames #200, 300 and 400 from a 463 millisecond sequence of
a bright Leonid meteor at 10:48:59 UT, November 18. These are false-
color images. The originals are in black-and-white only. The red color
is chosen arbitrarily to highlight contrast. The frames are cropped in
horizontal direction. The vertical field of view is about 6 degrees.
The meteor starts as a very localized ball. Then it brightens and
develops a tail, and one can clearly see the shock set up around the
front.
"Our images for the first time confirm that most meteor light comes
from a bright plasma just behind the meteoroid," says Leonid MAC PI
Dr. Peter Jenniskens of the SETI Institute at NASA Ames Research
Center. This confirms conclusions made indirectly from spectroscopic
studies in prior Leonid MAC missions. "The images now provide
dimensions of the gas cloud behind the meteoroid", says Jenniskens,
"and tell us how long organic molecules have to endure a hot plasma
before cooling down". Just behind the gas cloud, a wake develops
that is thought to be due to green forbidden line emission of OI at
557.2 nm.
Jenniskens believes that the bow shock may be a consequence of the
vapor cloud of ablated material surrounding the meteoroid growing
to sizes larger than the mean-free path in air at altitude. "This
emission may be responsible for some of the ionised emissions of Mg+
and Ca+ that are observed in bright Leonids", he says, "more so when
the meteoroids are larger". The pictures for the first time show the
meteor's bow shock.
The special Leonid storm session was organised by Jenniskens in
collaboration with Prof. Chet Gardner of the University of Illinois.
Presentations included this and other first results of the 2001
Leonid campaign, new modeling of meteor physical processes, studies
of the erosion of organic matter in meteoric plasma, the expected
mass distribution of Leonid meteoroid fragments, and the announcement
that tiny 1 nm sized dust grains of recondensed vapor may now have
been detected in the upper atmosphere.
[NOTE: Images supporting this release are available at
http://leonid.arc.nasadot gov/recent_updates6.html]
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