McDonald Observatory data on the comet Shoemaker-Levy 9 impacts on Jupiter and the resulting haze particles

Abstract

Simultaneous light curves of the Comet Shoemaker-Levy 9 fragment R and V impacts were measured with the McDonald Observatory 2.7 m and 0.8 m telescopes, at wavelengths of 2.12 μm and 0.893 μm, respectively. The R impact was clearly detected at 2.12 μm, but not at 0.893 μm, leading to an upper limit on the “main event” temperature of 1300 K. The V impact was not detected. A possible detection of the U impact at 2.12 μm was recorded. CCD spectrophotometry of Jupiter was obtained with the McDonald 2.1 m telescope during the Shoemaker-Levy 9 impact period (17 July–23 July 1994 UT; Barker et al. (1994) Bull. Am. Astron. Soc. 26, 1569). Spectra of Jupiter from 0.55 to 1.08 μm (10 Å resolution) were obtained using a long-slit CCD spectrograph (ES2), with a seeing-limited spatial resolution of about 1–2″. Impact regions were darker than neighboring non-impact regions by some 5–10% at all wavelengths except in the strong methane absorption bands (0.727, 0.864, and 0.890 μm) where the impact sites are brighter. Aerosol models of this spectral change are examined. The grey absorption observed is not typical of a population of particles much smaller than the wavelength. Neither is the similar haze brightening seen in two methane bands of similar strength at 0.727 and 0.864 μm. Our radiative transfer models of the H and E impact aites favor broad particle size distributions, with a mean particle radius 〈 r〉 = 0.25 μm and a log-normal size distribution of width b ≈ 0.6. A constant imaginary refractive index of 0.006 in this wavelength range provides an adequate spectral fit to the H data, while an index of 0.012 better fits the E data. Additional ES2 Jupiter spectra from June 1995 with both “blue” (0.31–0.58 μm) and “red” (0.55–1.08 μm) gratings were obtained. Blue spectra and images still show some evidence for residual impact haze opacity near the impact latitudes; red spectra and images do not. Apparently sedimentation of the larger particles in a broad initial size distribution has removed the red opacity.