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K. J. Meech (U of Hawaii, IfA), R. L. Newburn (JPL)
81P/Wild 2 is the target for study by the STARDUST space mission which launches 2/99 and will return a sample of comet dust to Earth. 81P/Wild 2 was selected because of its newness as a Jupiter family comet and because of the discovery of a trajectory offering the low encounter velocity of only 6.1 km s-1. Observations over a wide range of heliocentric distances since 1987 have enabled us to greatly enhance knowledge of 81P/Wild 2, as required to mount a successful space mission. Observations that indicate residual cometary activity out to a heliocentric distance of r = 4.7 AU show that the brightness is fairly symmetric about perihelion with a peak near perihelion. Twelve sets of observations beyond that distance indicate that the nucleus of 81P/Wild 2 is fairly spherical with a radius of 2.87 km (for pR = 0.02). No significant brightness variations attributable to rotation were seen during a 1 hour time-span on 1989 Aug 2, implying either a very spherical nucleus or relatively long period. Additional observations are scheduled for 1998 September to attempt to determine the rotation period (r = 4.01 AU) and we will report on this data. The color of the dust in the coma remained fairly constant at R-I=0.45 during 4 runs from r = 1.69-3.99 AU. The data at r = 1.58 AU showed a significantly bluer coma. Models for a flyby at 150 km closest approach to the nucleus, with an active surface area of 20% indicate that a spacecraft of 1 m2 cross section should be hit by one particle a bit larger than a mm in radius, and there are only about three chances in a 1000 of being hit by a particle 1 cm in radius or larger. This assumes the particle size distribution as measured for 1P/Halley (McDonnell {\it et al.} (1991), in {\it Comets in the Post-Halley Era}).