Monte-Carlo and multifluid modelling of the circumnuclear dust coma II. Aspherical-homogeneous, and spherical-inhomogeneous nuclei

Abstract

We use our newly developed Dust Monte-Carlo (DMC) simulation technique [Crifo, J.F., Lukianov, G.A., Rodionov, A.V., Zakharov, V.V., 2005. Icarus 176, 192–219] to study the dynamics of dust grains in the vicinity of some of the benchmark aspherical, homogeneous cometary nuclei and of the benchmark spherical, inhomogeneous nuclei studied by us precedingly. We use the interim unrealistic simplifying assumptions of grain sphericity, negligible nucleus rotation rate, and negligible tidal force, but take accurately into account the nucleus gravitational force, gas coma aerodynamic force, and solar radiation pressure force, and consider the full mass range of ejectable spherical grains. The resulting complicated grain motions are described in detail, as well as the resulting complicated and often counter-intuitive dust coma structure. The results are used to answer several important questions: (1) When computing coma dust distributions, (a) is it acceptable to take into consideration only one or two of the above mentioned forces (as currently done)? (b) to which accuracy must these forces be known, in particular is it acceptable to represent the gravity of an aspherical nucleus by a spherically symmetric gravity? (c) how do the more efficient but less general Dust Multi-Fluid (DMF) computations compare with the DMC results? (2) Are there simple structural relationships between the dust coma of a nucleus at small heliocentric distance r h , and that of the same nucleus at large r h ? (3) Are there similarities between the gas coma structures and the associated dust coma structures? (4) Are there dust coma signatures revealing non-ambiguously a spherical nucleus inhomogeneity or an homogeneous nucleus asphericity? (5) What are the implications of the apparently quite general process of grain fall-backs for the evolution of the nucleus surface, and for the survival of a landed probe?