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Dynamics and chemistry of SL9 plumes

Published online by Cambridge University Press:  02 August 2016

Kevin Zahnle
Kevin Zahnle*
Affiliation:
NASA Ames Research Center, M.S. 245-3, Moffett Field, California 94035-1000, USA

Abstract

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The SL9 impacts are known by their plumes. Several of these were imaged by HST towering 3000 km above Jupiter's limb. The heat released when they fell produced the famous infrared main events. The reentry shocks must have been significantly hotter than the observed color temperature would imply, which indicates that the shocks were radiatively cooled, and that most of the energy released on reentry was radiated. This allows us to use the infrared luminosities of the main event to estimate the energy of the impacts; we find that the R impact released some 0.3 — 1 x 1027 ergs. Shock chemistry generates a suite of molecules not usually seen on Jupiter. The chemistry reflects a wide range of different shock temperatures, pressures, and gas compositions. The primary product, apart from H2, is CO, the yield of which depends only weakly on the comet's composition, and so can be used to weigh the comet. Abundant water and S2 are consistent with a somewhat oxidized gas (presumably the comet itself), but the absence of SO2 and CO2 shows that conditions were neither too oxidizing nor the shocks too hot. Meanwhile, production of CS, CS2, and HCN appears to require a source in dry jovian air; i.e., the airbursts occurred above the jovian water table. Tidal disruption calculations and models of the infrared light curves agree on an average fragment diameter of about half a kilometer. Chemical products and atmospheric disruption models agree on placing the terminal explosions around the 1 to 4 bar levels. The plumes were spectacular because the explosions were shallow, not because the explosions were large.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 156: The Collision of Comet Shoemaker-Levy 9 and Jupiter , May 1996 , pp. 183 - 212
Copyright
Copyright © Cambridge University Press 1996

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