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Leonid MAC

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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 yellow-orange light.

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.


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