Thermal infrared imaging spectroscopy of Shoemaker-Levy 9 impact sites: Spatial and vertical distributions of NH3, C2H4, and 10-μm dust emission

Caitlin A. Griffith, Bruno Bézard, Thomas K. Greathouse, Douglas M. Kelly, John H. Lacy, Keith S. Noll

Research output: Contribution to journalArticle

56 Scopus citations

Abstract

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 NH3, C2H4, 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 × 17″ region generally centered on the K site and were composed of 0.8 × 1 arcsec pixels, each containing a spectrum of resolution ~15,000. We find evidence for two sources of NH3. Most of the stratospheric NH3resided at ~20 mbar. A second reservoir existed above 1 mbar, with a column abundance ~120lower than that of the deeper source (2 ± 1 × 1017molecules cm-2above 40 mbar for the K site). The position of the high altitude NH3suggests that it rose and was quenched within the fireball and survived the splash. The 2 ± 1 × 1013g of low altitude NH3indicates that the K impact upwelled at least ~2 × 1016g of jovian gas from Jupiter's troposphere. Its altitude coincides with the level where static stability is maximum. The NH3lineshape 12 days following impact indicates a gradual depletion of the high altitude source, which suggests that NH3was partially shielded from UV radiation. Enhanced continuum emission observed around 908 and 948 cm-1and not at wavenumbers outside the silicate feature is consistent with 8 ± 4 × 1012g of cometary dust residing in the plume fallback region. The total mass of C2H4was found to be 1 ± 0.3 × 1012g 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, C2H4, and HCN (B. Bézardet al.1997,Icarus125,94-120), observed at significantly lower pressures than NH3, covered a broader spatial extent, similar to the coverage of the ejecta blanket observed by HST. Six days following impact, the dust and C2H4spread 7° eastward of NH3, similar to the dark particulates. The quiescent behavior of the NH3at 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.

Original languageEnglish (US)
Pages (from-to)275-293
Number of pages19
JournalIcarus
Volume128
Issue number2
DOIs
StatePublished - Aug 1 1997
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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