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[11.03] Stratospheric NH₃ Following the SL9 Impacts with Jupiter: Abundance, Temperature, and Temporal Behavior

K. Fast, T. Hewagama (UMD at NASA/GSFC), T. Kostiuk, D. Deming, F. Espenak, P. Romani (NASA/GSFC), T. Livengood (CCSSE & NASA/GSFC)

Infrared emission lines of stratospheric NH₃ were observed at impact regions G and K following the collisions of Comet Shoemaker-Levy 9 with Jupiter in July of 1994. Spectra were obtained using an infrared heterodyne system at one of the Infrared Stellar Interferometer telescopes on Mount Wilson by Betz et al. Multiple lines of NH₃ were acquired on different post-impact days. Following an initial analysis, the spectra were analyzed using a beam-integrated radiative transfer software package developed at the Goddard Space Flight Center. A plume model was used to constrain post-impact temperature profiles.

One day following the G impact, the spectra indicate that the region had been heated to 250K above 0.01 mbar, and that the NH₃ was present at altitudes above a few mbar with a column density of 3.8 \times 10¹⁷ cm^-2. Three days later, the spectra indicate a temperature of 204K above a few tenths of a mbar, and no significant change was observed in the NH₃ distribution above 1 mbar. By 18 days post-impact, the G-region spectrum indicates NH₃ present below a few mbar with a column density of 3 \times 10¹⁸ cm^-2.

Comparison to photochemical models indicates that photolysis alone is not sufficient to account for the loss of NH₃ above a few mbar by that time. We speculate that the plume material dispersed at high altitude above 1 mbar is responsible for the spectra observed a few days post-impact. The 18-day observation appears to be dominated by the central impact region below 1 mbar which by that time had spread to fill the 2\arcsec instrument field-of-view. We will present these G-region results, along with the results of fits to 4- and 7-days post-impact K-region spectra.