COMET SHOEMAKER-LEVY-9 - AN ACTIVE COMET

The important elements of the debate over the activity versus dormancy of comet Shoemaker-Levy 9 (S-L 9) are reviewed. It is argued that the circularity of the isophotes in the inner comae of S-L 9 as well as t he spatial dependencies of the comae brightness profiles are indicator s of sustained dust production by S-L 9. It is also shown that the wes tward tail orientations, which were formerly interpreted as a sign of the comet's dormancy, are not a good indicator of either activity or d ormancy. Rather. the tail orientations simply place constraints on the dust production rate for grains smaller than approximate to 5 mu m. A ll the available evidence points to S-L 9 as having been an active, du st-producing comet. Synthetic images of an active comet are fitted to Hubble Space Telescope images of the S-L 9 fragment K, and its grain s ize and outflow velocity distributions are extracted. These findings s how that the appearance of the dust coma was dominated by large grains having radii between approximate to 30 mu m and approximate to 3 mm, produced at a rate of M over dot approximate to 22 kg s(-1), and eject ed at outflow velocities of approximate to 0.5m s(-1). Only upper limi ts on the production rates of smaller grains are obtained. The nucleus of fragment Ii was not observed directly but its size is restricted t o lie within a rather narrow interval 0.4 less than or similar to R-f less than or similar to 1.2 km. (C) 1997 Elsevier Science Ltd. All rig hts reserved.