On the stability of tangential discontinuity in the interaction of solar wind and cometary atmospheres

Abstract

ABSTRACT In 2004, European Space Agency launched the spacecraft Rosetta. After almost 10-yr flight it arrived at the Churyumova–Gerasimenko comet. Rosetta was orbiting about the comet for some time observing its environment. One of the most interesting observations obtained during this mission was multiple disappearance of magnetic field. It was suggested that this phenomenon is related to the instability of cometopause, which is a tangential discontinuity separating the solar wind flow from the plasma component of the flow from a comet. In this article, we aim to study this instability. We numerically calculated the stationary state with the account of charge exchange on water molecules and resonant charge exchange. Then, we solved the non-stationary problem using the stationary state as the initial condition. We also studied the stability of the cometopause analytically in the short-wavelength approximation where we substituted the curved cometopause by a tangent plane. Both the numerical and analytical results show that the velocity jump at the cometopause is too weak to overtake the stabilizing effect of the magnetic field and cause the Kelvin–Helmholtz instability. We conclude that the main course of the cometopause instability is the charge exchange, and the instability is similar to the Rayleigh–Taylor instability that occurs in a gravitational field.