Three-dimensional numerical simulations of the impact of Comet Shoemaker--Levy 9 on Jupiter and the resulting vapor plume expansion were conducted using the Smoothed Particle Hydrodynamics (SPH) method. An icy body with a diameter of 2 km can penetrate to an altitude of -350 km (0 km=1 bar) and most of the incident kinetic energy is transferred to the atmosphere between -100 km to -250 km. This energy is converted to potential energy of the resulting gas plume. The unconfined plume expands vertically and has a peak radiative power approximately equal to the total radiation from Jupiter's disc. The plume rises a few tens of atmospheric scale heights in ~102 seconds. The rising plume reaches the altitude of ~3000 km, but no atmospheric gas is accelerated to the escape velocity (~60 km/s). ¿ American Geophysical Union 1994