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LEONID DAILY NEWS: November 10, 2000


Meteoric debris is one of those elusive things that all know exist but nobody every seen it being made. Small fragments of the meteoroid that somehow survive the plunge into Earth's atmosphere. Meteoric debris in the form of small molten spherules are collected from Antarctic ice, accounting for about 4 percent of all extraterrestrial matter falling to Earth. Nobody until now has detected the creation of such debris where it occurs: in the path of a meteor.

Now, Jiri Borovicka and Peter Jenniskens report the first detection of debris in the afterglow of a bright fireball. This result is reported in an upcoming special issue of the journal "Earth, Moon and Planets".

Figures to the right show one frame from two video records of the spectrum. The animation below shows the video record from the BETSY spectrograph.

Spectrum of afterglow

Figure: Visible spectrum of the afterglow, after extraction.

During the 1999 Leonid Multi-Instrument Aircraft Campaign, while flying over the island of Corse, a fireball as bright as the full Moon appeared at 04:00:29 UT, November 18. The meteor left a bright glow intense enough to register on several slit-less spectrographs onboard the FISTA aircraft. The spectra show a series of parallel images, each representing the afterglow as seen in a specific color of light emitted by a single atomic species.

Video frame of afterglow spectrum

The emissions are interupted at least four times with a sharp edge, possibly the result of spinning of the meteoroid and an uneven breakup. The sharp edge of the first interuption was found to drop in altitude by as much as 1.5 kilometers in 1 second before coming to rest. Such descent points at significant downward flow along the meteoroid's path immediately after the collision.

The spectrum also shows a continuum emission that is the signature of solid matter. The shape and position of that red continuum implies a temperature of 1,400 K, which is the melting temperature of solid ("chondritic") comet matter. This is consistent with a process of secondary ablation, where atoms evaporate from small debris fragments that are left in the wake of the fireball. To our knowledge, this is the first time that the formation of meteoric debris at such high altitudes has been established.

The relative intensity of the atomic lines trace the gas temperature. Borovicka calculated that the gas cooled from 4,500 K to 1,200 K within 2 seconds. That appears to be fast enough to allow the debris to cool before complete evaporation (Full paper - PDF).

Previous news items:
Nov. 10 - Meteoroid debris detected
Nov. 09 - New meteor picture
Nov. 08 - Spin city
Nov. 07 - Meteors affect atmospheric chemistry
Nov. 06 - Listen to this!
Nov. 04 - Fear of heights?
Nov. 03 - The pale (infra-red) dot
Nov. 02 - Twin showers
Nov. 01 - Leonids approaching Earth
Oct. 31 - Prospects for Moon Impact Studies
Oct. 30 - Comet dust crumbled less fine
Today's news

These and other results of Leonid storm research will appear in a special issue of the peer-reviewed journal "Earth, Moon and Planets", published by Kluwer Academic Publishers, the Netherlands.

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