tunity to observe the effects of a sizable cometary collision on a major planet. But uncertainties as to the exact sizes
The observation of Comet Shoemaker-Levy 9's collision with
and densities of the impacting fragments (Weaver et al.
Jupiter in July of 1994 by the United Kingdom Infrared Telescope (UKIRT) produced spectroscopic data of high quality. 1995, Jewitt et al. 1993, Scotti and Melosh 1993) has made Analysis of the data for Impact C has produced the first temperinterpretation of the observations problematic. So in the ature curve that covers such an event, from the first visibility absence of absolute impact energies, Hammel et al. (1995) of the plume above the limb through to the settling down of devised a relative categorization making use of the obthe ejected gas onto the upper jovian atmosphere. Temperatures served effects. Their Class 1 impactors were Fragments G, derived from methane emission show that 5 min after impact, K, and L. These produced large ejecta and impact plumes a plume some 6500 km across was heated to ȁ1400 K. At its which reached a height of 3200 km above the ammonia maximum spatial extent ȁ12 min after impact, a region of ice cloud deck (taken as the zero point for height measure-Jupiter's atmosphere ȁ45,000 km west from the impact site of ments). According to Lagage et al. (1995), the peak intenthe main Fragment C nucleus was heated sufficiently to show sity from Fragment L was 13,000 Jy at 12 Ȑm. Impact sites methane emission. Observations of impact sites from one jovian visible immediately after collision stretched more than day onward showed that hot methane remained or was pro-10,000 km across and they probably produced multipleduced above the sites at least until July 27. © 1997 Academic Press wave events (although usually only one passing wave was clearly visible). Class 2 included Fragments A, C, E, and H and produced plume heights of about 2900 km, with
Introduction
''medium'' ejecta and 12-Ȑm peak intensities between 1200 The impact of Comet Shoemaker-Levy 9 (SL9) on Jupiand 2500 Jy (Lagage et al. 1995). Impact sites varied between 4000 and 8000 km in diameter. Class 3 comprised ter in July 1994 provided astronomers with a unique oppor-Fragments B, D, Q2, and N and produced almost no visible plume or ejecta. Impact sites were all less than 3,000 km