The nucleus of Comet P/Encke

The present CCD images and spectra of P/Encke near its aphelion during August-September 1988 indicates the cyclic character of the comet's brightness variation about a mean apparent red magnitude, with a photometric range of 0.62 + or - 0.04 mag. An aspherical rotating nucleus is judged to be consistent with (1) the observed cyclic variations, (2) the conformity of photometry with the inverse-square law, and (3) the absence of a resolvable coma. CCD spectra of the nucleus show a reddened continuum, in conjunction with a reflectivity gradient smaller than that of the nucleus of P/Tempel 2. 28 refs