Effects of Cosmic Rays on the Structure of the Heliosphere

The heliopause is a pressure balanced structure that separates the inner and outer heliosheaths. The total pressure of the solar wind particles, including pickup ions and anomalous cosmic rays (ACRs), is approximately equal to the pressure of the interstellar gas and its magnetic field on the outer side. Should one of the pressures change, the heliosphere will shrink or expand in response, to compensate for the imbalance and reach a new equilibrium state. Based on Voyager 1 observations, some ACRs may have crossed the heliopause and escaped into the interstellar medium, providing a mechanism of energy transfer between the inner and outer heliosheaths that is not included in conventional MHD models. Here we evaluate the effect of ACR escape on the size and shape of the heliosphere using a simple model that includes an additional energy flux term across the heliopause. We show that this effect could be a possible explanation for the unexpectedly early heliopause encounter by Voyager 1.