Anisotropic non-stationary gas flow dynamics in the coma of comet P/Halley

Abstract

One of the major results from the Giotto and Vega observations was that the gas outflow from the nucleus should be far from being spherically symmetric. Rather, the areas of active outgassing are restricted to a small part of the nucleus surface on the sunlit side and — due to the rotation of the nucleus — sources should be turned on and off periodically. In this paper we present results from numerical model calculations which address two particular outflow patterns that may occur at comet Halley: (a) steady state outflow dominated by a strong gas source at the subsolar point and (b) steady state gas flow caused by a ring-like outgassing region. In both cases we find that the anisotropies introduced at the comet’s surface are maintained out to rather large distances, i.e. several thousand kilometers. In addition to the steady state solutions we discuss the transient stages of the gas flow immediately after onset or offset of the strong outgassing at the subsolar point.