THE COLLISION OF JUPITER AND COMET SHOEMAKER-LEVY-9

A simple description of the disruption and deceleration of 100-m- to 5 -km-diameter comets striking Jupiter is combined with numerical simula tions of the subsequent explosions to predict the fate of Comet Shoema ker-Levy 9. Kilometer-size objects of density 1 g/cm3 explode at about the 10-bar level; a fragment of the same diameter but of density 0.3 g/cm3 explodes at about the 2-bar level. Detailed numerical simulation s of the first 3 min of the explosion were performed using the astroph ysical hydrodynamics program ZEUS-3D. Our numerical simulations begin either with hot cylinders with dimensions suggested by the disruption and deceleration model or with an initial wake constructed from a movi ng line charge. In all cases, extensive plumes of hot gas are expelled from the atmosphere. The models with wakes evolve about twice as fast as the initially confined models. Models of both types generate simil ar pressure waves into the planet. Temperatures and negative hydrogen ion opacities were computed by solving a battery of Saha equations. Fo r atmospheric entry, light curves were computed assuming thermal radia tion by clean jovian air with a surface area consistent with the (chan ging) cross-sectional area of the impactor. On entry the largest bolid es could be very bright, possibly as bright as Jupiter for observers p laced to see them, although for kilometer-size impactors the luminosit y peak is obscured by clouds. The timescale is about 10 sec. For the f ireball, light curves were computed from the numerical simulations ass uming a grey atmosphere. Metals from the vaporized comet provide elect rons that dramatically increase the opacity of Jovian air at low tempe rature; the resulting effective radiating temperature of the fireball is of order 3000 K. The fireball rises through and above the atmospher e, brightening at first as its surface area increases, but later fadin g to invisibility as its temperature drops and its opacity plummets. T he timescale is about 100 sec. (C) 1994 Academic Press, Inc.