THE NUCLEUS AND INNER COMA OF COMET 46P WIRTANEN/

We report the detection of the nucleus of comet 46P/Wirtanen from anal ysis of images taken with the Planetary Camera (WFPC2) of the Hubble S pace Telescope (HST) on 28 August 1996. The high spatial resolution (a WFPC2 pixel projects to 50 km at the distance of the comet) allowed u s to separate the signal of the nucleus from that of the coma and to d etermine the Landolt V and R magnitudes of the nucleus. Assuming a sph erical body with a geometric albedo of 0.04 and a phase coefficient of 0.04 mag/deg, we derived a radius of 0.60 +/- 0.02 km. The color of t he nucleus is moderately red with a gradient of 10% per 1000 Angstrom at optical wavelengths. From the lightcurve data we derived a rotation al period of 6.0 +/- 0.3 hr and find that the ratio of the semi-axes o f the assumed ellipsoidal body must satisfy a/b greater than or equal to 1.2. From an analysis of the dust coma, we derived that A f rho is 23 cm and that the dust production rate is 4 kg sec(-1).