COMET SHOEMAKER-LEVY-9 - IMPACT ON JUPITER AND PLUME EVOLUTION

The impact of fragments of Comet Shoemaker-Levy 9 on Jupiter and the r esulting vapor plume expansion are investigated by conducting three-di mensional numerical simulations using the smoothed particle hydrodynam ics (SPH) method. An icy body, representing the cometary fragments, wi th 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 init ial kinetic energy of the fragment is transferred to the atmosphere be tween 50 km and 300 km below the 1-bar pressure level. The shock-heate d atmospheric gas in the wake is totally dissociated and partially ion ized. Scaling our SPH results to other sizes indicates that fragments larger than approximately 100 m in diameter can penetrate to below the visible cloud decks. The energy deposited in the atmosphere is explos ively released in the upward expansion of the resulting plume. The plu me preferentially expands upward rather than horizontally due to the d ensity gradient of the ambient atmosphere. It rises greater-than-or-eq ual-to 10(2) km in approximately 10(2) sec. Eventually the total atmos pheric mass ejected to above 1 bar is greater-than-or-equal-to 40 time s the initial mass of the impactor. The plume temperature at a radius approximately 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 remo te sensing instruments of the Galileo spacecraft. As the impact site r otates 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 risin g plume reaches approximately 3000 km altitude in approximately 10 min and will be visible from Earth. (C) 1994 Academic Press, Inc.