Assuming a fairly narrow distribution of velocities for ballistic trajectories, we can explain several of the features observed in our H lightcurve as well as in published lightcurves for the L impact. We can also explain some of the features in the near-infrared lightcurves. In particular, the time of the first detection of the plume at visible wavelengths is accounted for by 9 1 km/s ejecta, which comprise most of the plume and the 11-km/s ejecta are responsible for the second maximum in the CCD lightcurves. The 9-km/s ejecta are also responsible for the beginning of the second precursor seen at near-infrared wavelengths and for the main peak. The first maximum in CCD lightcurves is at its widest phase in height and the maximum amount of material is exposed to sunlight. A fraction of the plume, the portion with velocities lower than 9 km/s, is responsible for the minimum when it disappears from direct solar illumination in the descending part of the trajectory. The CCD emission in the second maximum originates at pressures 25 mbar and 35 mbar for the L and H impacts, respectively. The near-infrared peak occurs before the second maximum in the CCD lightcurves.
We note that further elucidation of these processes will be possible when additional synoptic observations of the H and L impacts at shorter wavelengths are considered. This will give us a better description of the thermal behavior of the ejecta from its continuum emission. Ultimately, the most quantitative progress will be made by extending these calculations to a spatially inhomogenous thermophysical model for the ejecta which is coupled with appropriate radiative transfer calculations. These can then be compared with Galileo and earth-based observations at a variety of wavelengths.
© European Southern Observatory (ESO) 1997
Online publication: May 26, 1998