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LEONID DAILY NEWS: November 13, 2000

Mid-Infrared spectrum of persistent train

Figure right: The measured mid-Infrared spectrum. Relative radiance is plotted versus wavelength between 3 and 5.5 micron.


The Leonid Multi-Instrument Aircraft Campaing is NASA's first astrobiology mission. Its mission is to study the link between the abundant organic matter found in comets and interstellar matter in space, and the terrestrial environment that generated life on our planet.

Potential new ways of bringing organic matter to Earth by ways of meteor ablation were reported on earlier. Now, in today's issue of Earth, Moon and Planets Ray Russell, George Rossano, Mark Chatelain, David Lynch, Ted Tessensohn, Eric Abendroth and Daryl Kim of The Aerospace Corporation and Peter Jenniskens of the SETI Institute, at NASA Ames Research Center, report on a different manner how organic matter may have survived the plunge into Earth's atmosphere.

Pointing their infrared telescope at the persistent train in the path of the Y2K fireball, they discovered the fingerprint of complex organic matter: the C-H stretch vibration band at 3.4 micron. In addition a continuum emission was observed, possible from warm dust, and an emisison band that is caused by warm CO molecules in the path of the meteor.

Model spectrum for warm CO emission

Figure: The model spectrum for warm CO emission.

The organic C-H band is not well resolved, but it has much the same shape as the organic matter found in the dust of comets. This suggests that the organic matter survived more or less in-tact. Other instruments deployed during the mission showed that the fireball left meteoric debris behind. Organic matter in comet dust is intimately mixed with mineral grains. Hence, the observations suggest that organic matter can survive in the meteoric debris after deposition in the atmosphere.

It is possible, however, that trace air compounds such as methane cause the C-H stretch vibration band. The reason why this feature is a fingerprint of complex organic matter, is because all molecules containing C-H2 or C-H3 tend to absorp and emit light at this point in the spectrum. The methane molecule does so as well. Although the band shape is expected to be different, further modelling and analysis of more of the data is required to exclude any contribution from such source. Finally, rather than trace air compounds, the methane might be formed if the meteor material could have been broken down into atomic species and then formed into the observed molecules. All these alternatives need further study.

Cabon monoxide (CO) was detected with certainty. The CO molecule could be a trace air compound, but can also be created from atmospheric carbon dioxide CO2 in the path of the meteor. The model calculations left show that the CO molecules have a temperature of about room temperature (300K) at the time of the measurement several minutes after the fireball, some 50 degrees above the ambient temperature at that altitude. That temperature is consistent with earlier measurements of the sodium atom temperature by LIDAR and the temperature decay measured from the meteoric metal atom emissions (Full paper - PDF)

Previous news items:
Nov. 13 - Organic fingerprint
Nov. 12 - Train airglow chemistry
Nov. 11 - Hard bits and persisting glows
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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