Thermal infrared imaging spectroscopy of Shoemaker-Levy 9 impact sites: Temperature and HCN retrievals

Bruno Bézard, Caitlin A. Griffith, Douglas M. Kelly, John H. Lacy, Thomas Greathouse, Glenn Orton

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33 Scopus citations


We present high-resolution 8-14 μm observations of Shoemaker-Levy 9 sites conducted on July 20, 30, and 31 1994 UT at the NASA Infrared Telescope Facility. Stratospheric heating was detected from strong enhancements of methane emission near 8.1 μm over areas at least 15,000 km wide around the K site observed 23 hr after impact and around the L site 11 hr after impact. The intensity distribution between strong and weaker CH4lines implies that the stratospheric heating was primarily confined to pressures less than 500 μbar. The L site temperature increased by 80 ± 10 K at 5 μbar, but did not exceed 20 K around 1 mbar or 10 K around 10 mbar. The older K site was still 30 ± 5 K warmer than the surroundings at the 10-μbar level. The excess thermal energy stored in the upper jovian stratosphere was 3+3-1.5× 1026erg over the L site, and 2+2-1× 1026erg over the K site at the time of the observations. Comparison with numerical simulations indicates that a large fraction (<20%) of the kinetic energy of the L plume was transferred to the jovian atmosphere and not immediately radiated away. Acetylene line emission near 13.4 μm was enhanced over an area ~18,000 km wide centered on the E site 2.6 days after impact. Radiative transfer models of this emission indicate temperatures 37 ± 7 K higher than nominal around 3 μbar. No such enhancement was seen in CH4spectral images, implying that the temperature perturbation did not significantly extend below the ~20-μbar level. The H site observed simultaneously was 12 ± 5 K warmer than the surroundings 1.4 day after impact. C2H2lines were still slightly more intense over the K + W and Q1 sites on July 30 and 31, 8 to 10 days after impact. These observations can be interpreted either by temperature differences of about 13 and 10 K respectively in the 3-μbar region, or by an increase in the C2H2column density of 2.5-5 × 1017molecule cm-2. Emission from hydrogen cyanide lines around 13.4 μm was detected over all sites observed. The mass of HCN is about 2 × 1012g for the biggest plumes (K, L, G), 0.95 ± 0.5 × 1012g over the E site, and 0.45 ± 0.2 × 1012g over the H site. The total mass of HCN produced by all fragments is estimated to be 1.1 ± 0.4 × 1013g. A consistent interpretation of the different pieces of information available suggests that the H $cl10$plume was richer in dust than the E or A plume.

Original languageEnglish (US)
Pages (from-to)94-120
Number of pages27
Issue number1
StatePublished - Jan 1997

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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