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

Abstract

We have run high-resolution, three-dimensional, hydrodynamic simulations of the impact of comet ShoemakerLevy 9into the atmosphereof Jupiter.Wefindthat the energydeposition profile islargely similar to theprevious twodimensional 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 considerablesensitivityintheresultstosmallchangesintheinitialconditions,indicatingdynamicalchaos.Wecalculated 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 � ¼ 0: 6gc m � 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 diameterbolide), but the shreddedremains haveenoughinertia to carry themdownanother scale heightor 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 forthedifferentkinds of objects, or a scale-dependentbreakup phenomenology, with the preferred scaledependingonimpactordensity.Modelsofimpactorscoveringa � 600-foldrangeofmass(m)showthatlarger 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 . Subject headingg comets: individual (Shoemaker-Levy 9) — hydrodynamics