IMAGING OF ASTEROID 4179-TOUTATIS WITH THE HUBBLE-SPACE-TELESCOPE

We obtained four images of the asteroid 4179 Toutatis during its close approach to the Earth on 10 December 1992 with the planetary camera of the Hubble Space Telescope. The distance between the Earth and Toutatis at the time of our observations was 0.0291 AU (4.35 x 10(6) km); a single planetary camera pixel width subtends a distance of 996 meters at this distance. The solar phase angle was 91.3 degrees. Analysis of both raw and deconvolved images indicate that Toutatis was marginally resolved by the HST. There is evidence for an extended object with a projected illuminated dimension less than 2.8 km while the best fit symmetric model has a maximum illuminated size of 2.0 km and deconvolutions suggest an irregular object with a maximum dimension of 1.7 km, Our size determination is in good agreement with groundbased infrared radiometric size estimates. Our observations occurred near a local peak in the lightcurve and photometric points extracted from our images show that there were no rapid changes in brightness during the time we observed. The combination of a local peak in the lightcurve and our derived upper limit on the size places some constraints on possible shape models of Toutatis. (C) 1995 Academic Press, Inc.