8732( 1) - 12/30/99 12:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8732 Version: 1 Check-in Date: 30-Dec-1999 12:30:36 1.Proposal Title: Understanding the Physical Structure of the Comet Shoemaker-Levy 9 Fragments ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle AR 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Terrence Rettig University of Notre Dame CoI: Dr. Derek Richardson University of Washington N CoI: Sean Brittain University of Notre Dame N ------------------------------------------------------------------------------------ 5. Abstract Images of the fragmented comet Shoemaker--Levy 9 (SL9) as it approached Jupiter in 1994 provided a unique opportunity to (1) probe the comae, (2) understand the structure of the 20 cometary objects, and (3) provide limits on the Jovian impact parameters. The primary cometary questions were: how were the fragments formed and what was their central structure? There still remains a diversity of opinion regarding the structure of the 21 comet-like fragments as well as the specifics of the disruption event itself. We have shown from Monte Carlo modeling of surface brightness profiles that SL9 fragments had unusual dust size distributions and outflow velocities. Further work of a preliminary nature showed some of the central reflecting area excesses derived from surface brightness profile fitting (w/psf) appeared distributed rather than centrally concentrated as would be expected for comet- like objects, some central excesses were negative and also, the excesses could vary with time. With an improved coma subtraction technique we propose to model each coma surface brightness profile, extract central reflecting areas or central brightness excesses for the non-star-contaminated WFPC-2 SL9, to determine the behavior and characteristics of the central excesses as the fragments approached Jupiter. A second phase of the proposal will be to use numerical techniques (in conjunction with D. Richardson) to investigate the various fragment models. This is a difficult modeling process that will allow us to model the structure and physical characteristics of the fragments and thus constrain parameters for the Jovian impact events. The results will be used to constrain the structure of the central fragment cores of SL9 and how the observed dust comae were produced. The results will provide evidence to discriminate between the parent nucleus models (i.e., were the fragments solid objects or swarms of particles?) and provide better constraints on the atmospheric impact models. The physical characteristics of cometary nuclei are not well understood and the SL9 data provides an important opportunity to constrain these parameters. ------------------------------------------------------------------------------------ 8732( 1) - 12/30/99 12:59 - [ 2] Summary Form for Proposal 8732 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category AR ------------------------------------------------------------------------------------------------------------------------------------