Stratospheric Ammonia on Jupiter after the SL9 Collision

Abstract

We report results from measurements of NH3emission lines from the stratosphere of Jupiter following the impacts of fragments of Comet P/Shoemaker–Levy 9. Measurements were taken at the NASA Infrared Telescope Facility on 29 July 1994 on two impact regions, Q1 and the RSG complex, ∼8 days after the impacts. Emission line profiles were obtained near 11.2 μm at sub-Doppler spectral resolution (λ/Δλ ∼ 106). The measurements of the lineshapes permit the retrieval of NH3abundance and provide constraints on its altitude distribution in the stratosphere. If a uniformly mixed altitude distribution is assumed above the tropopause, the retrieved NH3mole fractions are 7.8 ± 1.6 × 10−9for the Q1 impact region and 4 ± 0.8 × 10−9for the RSG impact region. The total derived mass of NH3, ∼4 × 1012g within our field of view, is approximately 20 times greater than that possible from cometary origin. Near the Q1 impact site, ammonia emission is found to originate primarily from altitudes above the 10 mbar level, with a mole fraction of 18 ± 4 × 10−9corresponding to a column abundance of 2 ± 0.4 × 1016cm−2. Results are compared with other infrared and ultraviolet measurements and with recent photochemical models for jovian stratospheric NH3. These comparisons provide evidence for the presence of haze up to the 10 mbar level and provide an initial data set for study of the temporal behavior of NH3in the stratosphere of Jupiter.