Computer Science
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997icar..128..275g&link_type=abstract
Icarus, Volume 128, Issue 2, pp. 275-293.
Computer Science
16
Scientific paper
Spatially resolved spectroscopy of the Shoemaker-Levy 9 (SL9) sites traces the dynamical evolution of cometary material, upwelled tropospheric gas, and compounds produced when the plume splashed back upon the atmosphere. The emissions of impact-produced stratospheric NH_3, C_2H_4, and dust were imaged at NASA's Infrared Telescope Facility, with Irshell (the U. Texas mid-IR echelle spectrometer) 21 hr and 6, 11, and 12 days following the K impact. The images covered a ~7 x 17'' region generally centered on the K site and were composed of 0.8 x 1 arcsec pixels, each containing a spectrum of resolution ~15,000. We find evidence for two sources of NH_3. Most of the stratospheric NH_3 resided at ~20 mbar. A second reservoir existed above 1 mbar, with a column abundance ~1/20 lower than that of the deeper source (2 +/- 1 x 10^17 molecules cm^-2 above 40 mbar for the K site). The position of the high altitude NH_3 suggests that it rose and was quenched within the fireball and survived the splash. The 2 +/- 1 x 10^13 g of low altitude NH_3 indicates that the K impact upwelled at least ~2 x 10^16 g of jovian gas from Jupiter's troposphere. Its altitude coincides with the level where static stability is maximum. The NH_3 lineshape 12 days following impact indicates a gradual depletion of the high altitude source, which suggests that NH_3 was partially shielded from UV radiation. Enhanced continuum emission observed around 908 and 948 cm^-1 and not at wavenumbers outside the silicate feature is consistent with 8 +/- 4 x 10^12 g of cometary dust residing in the plume fallback region. The total mass of C_2H_4 was found to be 1 +/- 0.3 x 10^12 g and remained constant within error limits throughout the observations. The compounds above 1 mbar displayed differing horizontal coverages consistent with each molecule's role in a ballistic plume, having a range of temperatures. Ammonia at 20 mbar spread out with time; however, its coverage was never as extensive as that of the dark material seen in HST images. In contrast, the dust, C_2H_4, and HCN (B. Bezard et al. 1997, Icarus 125, 94-120), observed at significantly lower pressures than NH_3, covered a broader spatial extent, similar to the coverage of the ejecta blanket observed by HST. Six days following impact, the dust and C_2H_4 spread 7 deg eastward of NH_3, similar to the dark particulates. The quiescent behavior of the NH_3 at 20 mbar in contrast to the zonal drift of the dust indicates the presence of winds above 1 mbar that are disconnected from those in the lower stratosphere.
Bezard Bruno
Greathouse Thomas K.
Griffith Caitlin A.
Kelly Douglas M.
Lacy John H.
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