HST observations of the inner coma of Comet Levy 1990c.

Abstract

Comet Levy 1990c was observed by the Hubble Space Telescope on 27 September 1990, thus allowing to test data reduction procedures which will allow to model the nucleus of future targets of cometary space missions. The authors observe faint hemispherical shells expanding in the coma, which is structured as a sunward fan deflected by solar radiation pressure. The Eddington fountain model allows to infer the ejection times of the expanding shells and the initial velocity of the dust. The observed time periodicities suggest a nucleus rotating in 24 h with a surface characterized by two active areas placed almost exactly in opposite hemispheres.