Aug 28, 2003 -
NASA AMES RESEARCH CENTER, CA.
Many observers of last year's Leonid storms noticed the lingering trains
in bright fireballs that sometimes persist for an hour. Scientists
meeting at NASA Ames Research Center this week to discuss all aspects
of Leonid storm research have announced that the early fragmentation of
the comet rubble high in the Earth's atmosphere may be responsible for
the peculiar pattern of parallel tracks seen in many lingering trains.
"The early breakup could be due to the violent loss of volatile organic
molecules", says SETI Institute meteor astronomer Peter Jenniskens.
"Such loss of volatiles can lead to chemically altered products that may
have played a role in the origin of life".
Writing in a recent issue of WGN, the Journal of the International Meteor
Organization, Jenniskens points out that a catastrophic breakup often
leads to two large fragments, breaking off from the back of the meteoroid,
in the wake of much smaller debris. He explains: "Only the bigger chunks are
expected to induce the air turbulence that facilitates the mixing of oxygen atoms
in the train and ambient ozone molecules." The resulting chemical reaction
is catalyzed by meteoric iron atoms that end up shining bright in an eerie
Jenniskens finds that the Leonid meteoroids fall apart in the thin atmosphere
at altitudes of 160 - 120 km (100 - 75 miles) above the surface. By the time
that the rubble penetrates down to altitudes where ozone is abundant,
at 90 - 70 km (60 - 40 miles), those fragments can have moved apart
by several hundred meters. The separation of their turbulent wakes is further
enhanced by the pressure of the hot air in the meteor path, resulting in the
parallel bands of light that are common in lingering trains.
Earlier explanations for the structure of lingering trains assumed their
shape to be a hollow cylinder. This notion fell flat when it was found that
no light emanates from the space between the suspected cylinder walls.
This result is just one among many discussed at the 2003 Leonid MAC
Workshop, an international science meeting on the Leonid meteor storms,
which continues at NASA Ames Research Center until Saturday August 30.