Dust Outflow Velocity of Comet Shoemaker-Levy 9

Abstract

Tidal dispersal of the dust comae of the ∼21 fragments of Comet Shoemaker-Levy 9 (S-L 9) became very pronounced in Hubble Space Telescope observations during the weeks prior to impact with Jupiter (T. W. Rettig, J. Hahn, S. C. Tegler, M. Mumma, and M. DiSanti 1994a,Periodic Comet Shoemaker-Levy 9(1993e), IAU Circular 6028; H. A. Weaver plus 20 others 1995,Science267, 1282-1287). The degree of tidal dispersal experienced by the dust comae is quantified by calculating the coma flux as a function of distance from the center of a coma in both the jovian and transverse directions. The ratio of the jovian brightness profile to the transverse brightness profile for each fragment coma yields a quantity with approximately constant slope which we define as theJ/Tindex. The scale of this tidal dispersal is a function of the dust grain outflow velocity and distance from Jupiter. TheJ/Tindex combined with Monte Carlo tidal dust models is used to constrain the dust outflow velocity to 0.4 ± 0.1 m/sec for the dust seen in the preimpact images of June and July 1994. The HST images also show that as the S-L 9 comae approached Jupiter the central brightnesses decreased. The models indicate that the increasing tidal dispersal of the inner comae dust can only partially explain the observed decreases in brightness.