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KAO Observations of Fragment RVW Impacts


KAO Observations of Fragments R, V, and W into Jupiter, July 21-22, 1994

Hunten, Sprague, Witteborn, Kozlowski and Wooden used the High Efficiency Faint Object Infrared Grating Spectrometer (HIFOGS) to observe the impacts of fragments R, V, and W with the KAO. Because of the timing of the impacts, we observed the V site about an hour after the fragment crash time. We were on target at the time of the W impact, the final one in the series. Both sites were readily detected in the long and short wavelength channels of HIFOGS. The obvious things in the spectra are methane, ethane and acetylene. We think that these gases, already in the atmosphere, were lighted up by a huge, warm bubble of air heated by the dissipation of the energy following the explosion of the cometary fragments. Emissions from methane increased to about ten times the pre-impact value. The ethane and acetylene emissions also increased by many factors. During the R event the intensity at short wavelengths (methane) faded in about 20 minutes; at longer wavelengths (ethane and acetylene) the spectacular emission lines lasted a couple of hours. The more rapid disappearance of the emissions at shorter wavelengths, and the general fading, are probably explained by the cooling of the bubble as it expands. We were able to make observations at these wavelengths because the KAO flies at 12,500m, above most absorbing molecules in the Earth's atmosphere. Interestingly enough, the cometary fragments seemed to be exploding and depositing their energy at almost the same pressure level in Jupiter's atmosphere.

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