Abstract
A simple description of the disruption and deceleration of 100-m-
to 5-km-diameter comets striking Jupiter is combined with numerical
simulations of the subsequent explosions to predict the fate of Comet
Shoemaker-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
simulations of the first 3 min of the explosion were performed using
the astrophysical 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 moving 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 similar pressure waves into the planet. Temperatures
and negative hydrogen ion opacities were computed by solving a battery
of Saha equations. For atmospheric entry, light curves were computed
assuming thermal radiation by clean jovian air with a surface area
consistent with the (changing) cross-sectional area of the impactor.
On entry the largest bolides could be very bright, possibly as bright
as Jupiter for observers placed to see them, although for kilometer-size
impactors the luminosity peak is obscured by clouds. The timescale
is about 10 sec. For the fireball, light curves were computed from
the numerical simulations assuming a grey atmosphere. Metals from
the vaporized comet provide electrons that dramatically increase
the opacity of Jovian air at low temperature; the resulting effective
radiating temperature of the fireball is of order 3000 K. The fireball
rises through and above the atmosphere, brightening at first as its
surface area increases, but later fading to invisibility as its temperature
drops and its opacity plummets. The timescale is about 100 sec. (C)
1994 Academic Press, Inc.
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