Comet Shoemaker-Levy 9: Impact on Jupiter and Plume Evolution
The impact of fragments of Comet Shoemaker-Levy 9 on Jupiter and the resulting vapor plume expansion are investigated by conducting three-dimensional numerical simulations using the smoothed particle hydrodynamics (SPH) method. An icy body, representing the cometary fragments, with a velocity of 60 km/sec and a diameter of 2 km can penetrate to 350 km below the 1-bar pressure level in the atmosphere. Most of the initial kinetic energy of the fragment is transferred to the atmosphere between 50 km and 300 km below the 1-bar pressure level. The shock-heated atmospheric gas in the wake is totally dissociated and partially ionized. Scaling our SPH results to other sizes indicates that fragments larger than ∼100 m in diameter can penetrate to below the visible cloud decks. The energy deposited in the atmosphere is explosively released in the upward expansion of the resulting plume. The plume preferentially expands upward rather than horizontally due to the density gradient of the ambient atmosphere. It rises ≥10^2 km in ∼10^2 sec. Eventually the total atmospheric mass ejected to above 1 bar is ≥40 times the initial mass of the impactor. The plume temperature at a radius ∼10^3 km is >10^3 K for 10^3 sec for a 2-km fragment. We predict that impact-induced plumes will be observable with the remote sensing instruments of the Galileo spacecraft. As the impact site rotates into the view of Earth some 20 min after the impact, the plume expansion will be observable using the Hubble Space Telescope and from visible and infrared instruments on groundbased telescopes. The rising plume reaches ∼3000 km altitude in ∼10 min and will be visible from Earth.
© 1994 Academic Press Inc. Revised February 9, 1994; revised April 25, 1994. Available online 24 April 2002. Research supported by NASA and Cray Research Corp. All the SPH calculations are carried out on the CRAY-YMP at Jet Propulsion Laboratory. We thank W. W. Anderson for comments on this paper. We thank B. Sturtevant, D. A. Crawford, M. M. Mac Low, W. Benz, A. M. Vickery, H. Kanamori, A. P. Ingersoll, D. J. Stevenson, J. Friedson, and K. Zahnle for helpful comments and M. Lainhart for his technical support. We thank M. B. Boslough, and an anonymous reviewer for improving the manuscript.