DUST ABLATION DURING THE SHOEMAKER-LEVY-9 IMPACTS

Because of the complexity of the physical and chemical processes that occurred during the collision of Comet Shoemaker-Levy 9 with Jupiter, our understanding of the observed phenomena is not complete. In this p aper, models of the ablation of small particles from both the incoming cometary comae and the refalling impact plumes are used to better def ine the physics and chemistry of the impacts. The incomplete ablation of small refractory plume grains can explain both the timing and relat ive strengths of the metal emission lines (e.g., Mg and Na) that were observed many minutes after the impacts. Model-data comparisons show t hat silicate dust was present in the fastest moving portions of the pl ume and that some of the plume material (at least during the L impact) was ejected at velocities in excess of 22 km s(-1) (for a 45 degrees ejection angle). The models also show that the plume dust is not compl etely ablated at typical plume reentry velocities; therefore, a good e stimate for the maximum size of the plume grains is the final observed radius of the high-altitude dust (e.g., < 0.15 mu m), and abundances inferred from the metallic emission features observed after the impact s do not provide a good measure of the amount of silicate material in the plume. Other implications for the physical and chemical properties of the comet/impact plume and for the timing and other features of th e observations are discussed in detail.