A Test for Whether or Not Voyager 1 Has Crossed the Heliopause

Abstract:

The Voyager 1 (V1) 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, suggesting easy escape of the former across the heliopause, and entry of the latter. The question is, has V1 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 V1 is unchanged from the direction of the heliosheath magnetic field, and is in a substantially different direction from the expected direction of the interstellar magnetic field. However, observations of plasma oscillations and thus of the plasma electron density argue that the densities are comparable to the densities expected in the interstellar medium. In this talk we present a model for the nose region of the heliosheath in which the high plasma densities are due to compressed solar wind and not interstellar gas, and thus both the observed magnetic field direction and the observed plasma density indicate that V1 remains in the heliosheath. The model has a simple test: we predict that V1 will encounter the heliospheric current sheet that marks the polarity reversal of the solar magnetic field before the end of 2015.