Voyager observations of the magnetic field in the heliosheath and the local interstellar medium

Abstract

This paper reviews observations of the magnetic field B in the heliosheath by Voyager 1 (V1) and Voyager 2 (V2) and the recent observations of the LISM by V1. The heliosheath is the region between the termination shock (TS) and the heliopause (HP). The TS was identified by both V1 and V2, and the internal structure of the TS was determined by V2. The radial distance of the TS was 94 AU at V1 and 84 AU at V2, suggesting a global asymmetry of the heliosphere. The average direction of B in the heliosheath is that of the Parker spiral magnetic field, and non-periodic magnetic sectors were observed by V1 and V2. The heliosheath is disturbed and turbulent, particularly just behind the TS, and it is described by the multifractal spectrum, the q-correlation function and the q-Gaussian distribution. The multifractal spectrum in the heliosheath also varies with the solar cycle. Voyager 1 has been in the LISM since at least August 25, 2012, but the nature of the HP and the time of the HP crossing not been determined. The magnetic field direction is close to, but distinguishable from the Parker spiral magnetic field, and its departure from the Parker spiral magnetic field is slowly increasing with distance from the sun. A large pressure pulse and two shocks or pressure waves have been identified in the LISM, presumably generated inside the heliosphere and transmitted through the heliosheath and heliopause. The interstellar magnetic field lines are draped across the heliopause, and B is approximately 0.5 nT. The fluctuations of B are very small but turbulent on scales 1 day to 468 days, with a Kolmogorov spectrum and an injection scale of approximately 10 pc.