A model for the nose region of the heliosheath

Abstract

The Voyager 1 spacecraft is currently in the vicinity of the heliopause, which separates the heliosphere from the local interstellar medium. There has been a precipitous decrease in particles accelerated in the heliosphere, and a substantial increase in galactic cosmic rays (GCRs), suggesting easy escape of the former across the heliopause, and entry of the latter. The question is, has Voyager 1 actually crossed the heliopause and is it now in the interstellar medium? Here the evidence is inconclusive. The direction of the magnetic field observed by Voyager 1 is essentially unchanged from the direction of the heliospheric magnetic field. However, the plasma density, which is measured from observations of plasma waves, is similar to the expected higher density of interstellar plasma. In this paper, the principal results of an analytic model are presented demonstrating that the higher plasma densities measured by Voyager 1 are likely to be compressed solar wind. Thus both the magnetic field and the plasma density observations are consistent with Voyager 1 still remaining well within the heliosheath. The model has a simple test: Voyager 1 should encounter a current sheet crossing, where the behavior of particles accelerated in the heliosphere and the GCRs will be different from what Voyager 1 is now observing.