Plasma properties at the Voyager 1 crossing of the heliopause

Abstract

In August 2012, Voyager 1 crossed the heliopause at a distance of 121.5 AU from the Sun. It is argued that the spacecraft entered a region in the outer heliosheath that had the characteristics of a plasma depletion layer. Observed plasma parameters at the heliopause, properties of plasma depletion layers, and some assumptions are used to derive a set of plasma parameters on both sides of the heliopause. Using the density, temperature, and magnetic field magnitude on each side, the corresponding plasma beta and Alfven Mach number (in the outer heliosheath) are derived. These plasma parameters are used to demonstrate that the plasma depletion process is occurring in the outer heliosheath adjacent to the heliopause and these parameters are used to determine if lower hybrid waves are generated locally and if magnetic reconnection is occurring locally at the location of the Voyager 1 crossing. Reconnection may not be an effective source of superthermal electrons at the heliopause, based on the small Alfven speeds there (VA ≤ 100 km/s) and an empirical connection between electron heating and Alfven speed found in inner solar system studies.