The Global Morphology of the Solar Wind Interaction with Comet Churyumov-Gerasimenko

Abstract

The forthcoming Rosetta-Philae mission to comet 67P/Churyumov-Gerasimenko provides a novel opportunity to observe the variable nature of the solar wind interaction with a comet over an extended range of heliocentric distance. We use a simple analytical one-dimensional MHD model to estimate the sizes of the two most prominent features in the global structure of the solar wind interaction with a comet. When the heliocentric distance of the comet reaches d <= 1.51 AU, we expect a sharp shock to be observed, whose size would increase monotonically as the comet approaches the Sun, reaching a value ~= 15, 000 km at perihelion (d ~= 1.29 AU). Upstream of the shock, we expect the velocity-space distribution of the picked up cometary ions to be essentially gyrotropic. A well-defined ionopause is predicted when d <=1.61 AU, though its size is expected to be only sime25 km at perihelion, and it is expected to be susceptible to the "flute" instability due to its small size. Consequently, we expect the magnetic field to penetrate all the way to the surface of the nucleus. We conclude with a brief discussion of the response of the comet's plasma environment to fast temporal variations in the solar wind.