THERMAL INFRARED IMAGING SPECTROSCOPY OF SHOEMAKER-LEVY-9 IMPACT SITES - SPATIAL AND VERTICAL DISTRIBUTIONS OF NH3, C2H4, AND 10-MU-M DUST EMISSION

Spatially resolved spectroscopy of the Shoemaker-Levy 9 (SL9) sites tr aces the dynamical evolution of cometary material, upwelled tropospher ic gas, and compounds produced when the plume splashed back upon the a tmosphere. The emissions of impact-produced stratospheric NH3, C2H4, a nd dust were imaged at NASA's Infrared Telescope Facility, with Irshel l (the U. Texas mid-IR echelle spectrometer) 21 hr and 6, 11, and 12 d ays following the K impact. The images covered a similar to 7 x 17'' r egion generally centered on the K site and were composed of 0.8 x 1 ar csec pixels, each containing a spectrum of resolution similar to 15,00 0, We find evidence for two sources of NH,. Most of the stratospheric NH3 resided at similar to 20 mbar, A second reservoir existed above 1 mbar, with a column abundance similar to 1/20 lower than that of the d eeper source (2 +/- 1 x 10(17) molecules cm(-2) above 40 mbar for the K site), The position of the high altitude NH3 suggests that it rose a nd was quenched within the fireball and survived the splash. The 2 +/- 1 x 10(13) g of low altitude NH3 indicates that the K impact upwelled at least similar to 2 x 10(16) g of jovian gas from Jupiter's troposp here, Its altitude coincides with the level where static stability is maximum, The NH, lineshape 12 days following impact indicates a gradua l depletion of the high altitude source, which suggests that NH3 was p artially shielded from UV radiation, Enhanced continuum emission obser ved around 908 and 948 cm(-1) and not at wavenumbers outside the silic ate feature is consistent with 8 +/- 4 x 10(12) g of cometary dust res iding in the plume fallback region. The total mass of C2H4 was found t o be 1 +/- 0.3 x 10(12) g and remained constant within error limits th roughout the observations. The compounds above 1 mbar displayed differ ing horizontal coverages consistent with each molecule's role in a bal listic plume, having a range of temperatures. Ammonia at 20 mbar sprea d out with time; however, its coverage was never as extensive as that of the dark material seen in HIST images, In contrast, the dust, C2H4, and HCN (B. Bezard et al. 1997, Icarus 125, 94-120), observed at sign ificantly lower pressures than NH3, covered a broader spatial extent, similar to the coverage of the ejecta blanket observed by HST, Six day s following impact, the dust and C2H4 spread 7 degrees eastward of NH3 , similar to the dark particulates, The quiescent behavior of the NH3 at 20 mbar in contrast to the zonal drift of the dust indicates the pr esence of winds above 1 mbar that are disconnected from those in the l ower stratosphere. (C) 1997 Academic Press.