THE HUBBLE-SPACE-TELESCOPE (HST) OBSERVING CAMPAIGN ON COMET SHOEMAKER-LEVY-9

The Hubble Space Telescope made systematic observations of the split c omet P/Shoemaker-Levy 9 (SL9) (P designates a periodic comet) starting in July 1993 and continuing through mid-July 1994 when the fragments plunged into Jupiter's atmosphere. Deconvolutions of Wide Field Planet ary Camera images indicate that the diameters of some fragments may ha ve been as large as similar to 2 to 4 kilometers, assuming a geometric albedo of 4 percent, but significantly smaller values (that is, <1 ki lometer) cannot be ruled out. Most of the fragments (or nuclei) were e mbedded in circularly symmetric inner comae from July 1993 until late June 1994, implying that there was continuous, but weak, cometary acti vity. At least a few nuclei fragmented into separate, condensed object s well after the breakup of the SL9 parent body, which argues against the hypothesis that the SL9 fragments were swarms of debris with no do minant, central bodies. Spectroscopic observations taken on 14 July 19 94 showed an outburst in magnesium ion emission that was followed clos ely by a threefold increase in continuum emission, which may have been caused by the electrostatic charging and subsequent explosion of dust as the comet passed from interplanetary space into the jovian magneto sphere. No OH emission was detected, but the derived upper limit on th e H2O production rate of similar to 10(27) molecules per second does n ot necessarily imply that the object was water-poor.