GALILEO NIMS DETECTS R IMPACT FIREBALL AND FALL BACK
The Near Infrared Mapping Spectrometer onboard Galileo has detected the R impact event fireball and the fall back of impact ejecta onto the Jovian atmosphere, in the final Shoemaker-Levy 9 data played back from the spacecraft in January 1995. The initial R detection is at 05:35:19 UT on July 21, 1994 (corrected to the time the event would have been seen on Earth). The fireball is only about 25% of the peak brightness of the G impact event previously seen (Carlson et al., Geophys. Res. Lett., submitted), and is clearly detected in only 3 NIMS scans, each separated by 10 2/3 seconds.
A second brightening in the infrared is seen by NIMS beginning 6 minutes and 0 seconds after the initial impact detection, and continuing to brighten for 200 seconds until the termination of the playback data. The peak brightness is about half of that seen for a similar secondary IR brightening after the G impact event. We interpret this event as the fallback of impact ejecta onto the Jovian stratosphere. This implies a minimum ejection velocity of 4.0 km/sec.
Detailed analyses of the R data are currently underway. No further playback of Galileo data from the Shoemaker-Levy 9 impacts is planned.
Robert Carlson, Paul Weissman, William Smythe, Marcia Segura, John Hui, Robert Mehlman, and Frank Leader
Galileo NIMS Team, Jet Propulsion Laboratory and UCLA
Feb. 10, 1995