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The fragments of Comet Shoemaker-Levy 9 will impact Jupiter during the period of 16--22 July 1994. Each impact will release between $10^{27}$ and $10^{30}$ ergs of kinetic energy into the Jovian atmosphere, depending on the size and density of the fragment. We have used a series of numerical calculations to model the first hour after entry of each fragment.
We begin with a model of the energy deposition in the atmosphere by the bolide. We used the astrophysical hydrocode ZEUS to follow the bolide during its descent through the Jovian atmosphere. We found that the numerical results were consistent with a simple analytic model of the quasi-static deformation of the bolide by ram pressure. Over 90% of the impact energy is released within one scale height, at a pressure of order 10 bars for a 1 km impactor. We use the energy deposition profile from our entry models as the initial conditions for larger-scale ZEUS models of the resulting explosions. These explosions are just large enough to drive a shock wave completely out of the atmosphere. The visible fireball lasts for one or two minutes, and the blowout of the shock takes only a minute or so longer. About an impactor mass of material will be ejected to altitudes of a few thousand km before falling back ballistically and spreading out along the top of the stratosphere. When the volatiles in this material condense, they may produce a detectable infrared signal. The downward moving shock wave from the explosion heats the troposphere as it decays into a sound wave. Some of this heated troposphere will rise above the cloud layers into the stratosphere where it will be spectroscopically observable, providing the first direct sample of the Jovian troposphere. The downward moving sound wave will carry a significant fraction of the impact energy and will probe the deep interior of the planet before refracting back to the surface.
ZEUS was provided by the Laboratory for Computational Astrophysics at the NCSA. Computations were performed at the PSC.. This work was supported by the NSF Aeronomy Program, and the NASA Programs in Astrophysical Theory and Exobiology.
