Structures in the coma of comet Halley

Abstract

Dense dust jets are expected to be encountered by the spacecraft penetrating the coma of comet Halley in March 1986. At the time of encounters, remote observations of the global distribution of coma constituents will complement the detailed in situ measurements. Here we report ground-based measurements of the optical brightness distribution of the coma, made in November 1985, when the comet was at a distance of 1.75 AU from the Sun. From the total brightness we deduce a dust production rate of 1.5 × 10⁶ g s⁻¹, but our results show that cometary dust and gas production, which seem to be correlated, are strongly anisotropic and time-variable. Structures in the coma can be revealed by comparison with a physical model of the coma, but astrometry of the comet nucleus is adversely affected by the anisotropic brightness distribution in the coma.