THE TIME SEQUENCE OF SL9 IMPACT-H AND IMPACT-L FROM INFRARED OBSERVATIONS

The light curve of the impact sites on Jupiter of the fragments of Sho emaker-Levy 9 exhibits some characteristic features, which have been r etrieved for several impacts, and must therefore correspond to differe nt steps in the release and dissipation of the kinetic energy deposite d during the impacts. Accurate geometric calculations are presented, w hich allow us to estimate the possible altitude of observable events i n the light curve. A radiative transfer calculation made at 3.5 mu m s hows that a hot spot in the atmosphere can indeed be observed at emiss ion angles as large as 95 degrees, at pressure levels of 10-100 mu bar s. Observations taken simultaneously on impact H and L between Pic-du- Midi observatory (imaging at 1-2 mu m), ESO/NTT (3.5 mu m imaging spec troscopy for H only) and NOT (imaging at 10 mu m), are analyzed to sea rch for wavelength variations in the light curve. It is found that the time of occurence of the precursor observed just before the main even t in the L light curve is shifted by approximate to 1 minute between 1 .2 and 10 mu m observations. The observations of the later stage (on i mpact H) show a similar shoulder in the decreasing part of the light c urve. A. spatial extension of the emissions could possibly explain the observations.