EVIDENCE ON SIZES AND FRAGMENTATION OF THE NUCLEI OF COMET SHOEMAKER-LEVY-9 FROM HUBBLE-SPACE-TELESCOPE IMAGES

Digital maps of the central regions of 13 nuclear condensations of Com et Shoemaker-Levy 9, obtained with the Wide Field Planetary Camera-2 o f the Hubble Space Telescope on January 24-25, March 28-30, and July 4 , 1994, were analyzed with the aim to identify the presence of distinc t, major fragments in each condensation, to deconvolve their contribut ions to the signal that also includes the contribution from a surround ing cloud of dust (modeled as an extended source, using two different laws), to estimate the dimensions of the fragments and to study their temporal variations, and to determine the spatial distributions of the fragments as projected onto the plane of the sky. The deconvolution m ethod applied is described, an extensive analysis of the errors involv ed is presented, and the results are summarized. They include the find ing that sizable fragments did survive until the time of atmospheric e ntry. This result does not contradict evidence of the comet's continui ng, apparently spontaneous fragmentation, which still went on long aft er the extremely close approach to Jupiter in July 1992 and which, bec ause of the Jovian tidal effects, may even have intensified in the fin al days before the crash on Jupiter. On plausible assumptions regardin g the geometric albedo and the phase coefficient, the largest fragment s are found to have had effective diameters of similar to 4 km as late as March and even early July 1994. In most condensations, several siz able companions (similar to 1 km or more across) have been detected wi thin similar to 1000 km of the projected location of the brightest fra gment, and the surrounding dust cloud has been found to be centered on a point that is shifted in the general direction of the tail, most pr obably due to effects of solar radiation pressure.