Possible explanation of the secondary flash and strong flare on IR lightcurves upon impact of Shoemaker‐Levy 9

Observations of IR lightcurves of Comet Shoemaker‐Levy 9 impacts detected strong thermal emissions at most impact events. During several huge impacts such as C, K, and R events, two precursor flashes were detected before the strong emission (e.g., Graham et al., 1995; Watanabe et al., 1995). Comparison of IR lightcurves with Galileo and HST data suggests that the first flash should correspond to the entry of a comet. At K impact, the secondary flash started rising after 60sec from the first flash and the strong emission started after 350sec from the first flash. To understand the flashes and the strong thermal emission, we have performed direct numerical simulations of break‐up and subsequent explosion processes with highly accurate hydrocode. When the energy deposition length is quite long and is 300 km, two groups of materials are ejected and the two peaks corresponding to the secondary flash and strong thermal flare are obtained in the time evolution of density and temperature whose temporal profile agrees quite well with observations.