COMETS - GROUNDBASED OBSERVATIONS OF SPACECRAFT MISSION CANDIDATES

Several comet flyby and/or rendezvous missions are currently being planned, for which supporting groundbased data from previous apparitions should prove useful. Here, we discuss groundbased narrowband photometry obtained over the last 15 years for nine candidate comets, five of which have been observed on multiple apparitions. The comets observed include Churyumov-Gerasimenko, d'Arrest, Encke, Grigg-Skjellerup, Honda-Mrkos-Pajdusakova, Kopff, Tempel 1, Tempel 2, and Wild 2. We present production rates for OH and CN, as well as Afρ{variant} values as a measure of the dust production for each of the candidates. Expected values for both water and dust production rates are given for Comet P/Grigg-Skjellerup at the time of the upcoming Giotto encounter. Based on the measured OH production rates and a model of the sublimation of water from the surface, we derive limits on the size of each cometary nucleus. In order to facilitate spacecraft mission planning, we also present molecular abundance ratios, nore variations in cometary activity as a function of orbital position and between apparitions, and note the overall degree of dustiness. A detailed analysis of the characteristics of these nine viable mission candidates will provide necessary information for prioritizing targets for any future missions. Finally, the nine candidates are compared to Comet Halley and to a hypothetical "typical" comet as defined by Osip et al., 1992, (15 years of comet photometry: A comparative analysis of 80 comets. In Asteroids, Comets, and Meteors 1991, A. W. Harris and E. Bowell (Eds.) Lunar and Planetary Institute, Houston.). © 1992.