Micro-Structure of the Heliospheric Termination Shock.

Observations by the Voyager 2 spacecraft of the structure of the heliospheric termination shock revealed a quasi-perpendicular structure that possessed many of the characteristics that are familiar to us from perpendicular shocks observed in the inner heliosphere. However, a surprise was the relative lack of heating experienced by thermal solar wind ions (and electrons), leading to the suggestion that the pickup ions were primarily heated at the heliospheric termination shock. Because the Voyager plasma instrument cannot measure the interstellar pickup ions directly, their behavior at the termination shock could not be gauged directly. Nonetheless, it had already been predicted [16] that the primary dissipation mechanism for the quasi-perpendicular termination shock would be the reflection of pickup ions rather than solar wind ions; this because of the shell-like structure of the pickup ion distribution function. We discuss the effect of pickup ions including their trajectories within the structure of the shock observed by Voyager 2. A model for the shock structure is constructed on the basis of preferentially reflected pickup ions, solutions are discussed, and we estimate the degree of heating for the various components. [ABSTRACT FROM AUTHOR]