Shoemaker-Levy 9 Impact Modeling. I. High-Resolution Three-dimensional Bolides

We have run high-resolution, three-dimensional, hydrodynamic simulations of the impact of comet Shoemaker-Levy 9 into the atmosphere of Jupiter. We find that the energy deposition profile is largely similar to the previous two-dimensional calculations of Mac Low & Zahnle, although perhaps somewhat broader in the range of height over which the energy is deposited. As with similar calculations for impacts into the Venusian atmosphere, there is considerable sensitivity in the results to small changes in the initial conditions, indicating dynamical chaos. We calculated the median depth of energy deposition (the height z at which 50% of the bolide's energy has been released) per run. The mean value among runs is ~70 km below the 1 bar level, for a 1 km diameter impactor of porous ice of density ρ=0.6 g cm^-3. The standard deviation among these runs is 14 km. We find little evidence of a trend in these results with the resolution of the calculations (up to 57 cells across the impactor radius, or 8.8 m resolution), suggesting that resolutions as low as 16 grid cells across the radius of the bolide may yield good results for this particular quantity. Visualization of the bolide breakup shows that the ice impactors were shredded and/or compressed in a complicated manner but evidently did not fragment into separate, coherent masses, unlike calculations for basalt impactors. The processes that destroy the impactor take place at significantly shallower levels in the atmosphere (~-40 km for a 1 km diameter bolide), but the shredded remains have enough inertia to carry them down another scale height or more before they lose their kinetic energy. Comparison of basalt impactor models shows that energy deposition curves for these objects have much less sensitivity to initial conditions than do ice impactors, which may reflect differences in the equation of state for the different kinds of objects, or a scale-dependent breakup phenomenology, with the preferred scale depending on impactor density. Models of impactors covering a ~600-fold range of mass (m) show that larger impactors descend slightly deeper than expected from scaling the intercepted atmospheric column mass by the impactor mass. Instead, the intercepted column mass scales as m^1.2.