1998A&A...335L..25L

We report the detection of the nucleus of comet 46P/Wirtanen from analysis of images taken with the Planetary Camera (WFPC2) of the Hubble Space Telescope (HST) on 28 August 1996. The high spatial resolution (a WFPC2 pixel projects to 50 km at the distance of the comet) allowed us to separate the signal of the nucleus from that of the coma and to determine the Landolt V and R magnitudes of the nucleus. Assuming a spherical body with a geometric albedo of 0.04 and a phase coefficient of 0.04mag/deg, we derived a radius of 0.60±0.02km. The color of the nucleus is moderately red with a gradient of 10% per 1000Å at optical wavelengths. From the lightcurve data we derived a rotational period of 6.0±0.3hr and find that the ratio of the semi-axes of the assumed ellipsoidal body must satisfy a/b≥1.2. From an analysis of the dust coma, we derived that Afρ is 23 cm and that the dust production rate is 4kg/s.