Orbital evolution of impact ejecta from Ganymede

We have numerically computed the orbital evolution of similar to10(3) particles representing high-speed ejecta from Gilgamesh, the largest impact basin on Ganymede. The integration includes the four Galilean satellites, Jupiter (including J(2) and J(4)), Saturn, and the Sun. The integrations last 100,000 years. The particles are ejected at a variety of speeds and directions, with the fastest particles ejected at 1.4 times the escape speed v(esc) equivalent to root2GM(G)/R-G of Ganymede. Ejecta with speeds v < 0.96v(esc) follow suborbital trajectories. At v similar to 0.96v(esc) there is a transition characterized by complex behavior suggestive of chaos. For v > 0.96v(esc), most particles escape Ganymede and achieve orbits about Jupiter. Eventually most (similar to71%) of the jovicentric particles hit Ganymede, with 92% of these hitting within 1000 years. The accretion rate scales as I It. Their impact sites are randomly distributed, as expected for planetocentric debris. We estimate that most of the resulting impact craters are a few kilometers across and smaller. The rest of the escaping ejecta are partitioned as follows: similar to3% hit Io; similar to10% hit Europa; similar to13% hit Callisto; 2% reach heliocentric space; and less than similar to1% hit Jupiter. Only two particles survived the entire 10(5)-year integration. Ejecta from large impact events do not appear to be a plausible source of large craters on the Galilean satellites; however, such ejecta may account for the majority of small craters. (C) 2002 Elsevier Science (USA).