Chaotic collisionless reconnection in Jupiter's nightside magnetosphere

Abstract

Recently it has been shown that an X-type magnetic neutral line may form in Jupiter's nightside magnetosphere as the result of the current flowing in the plasma disc. Still, a collisionless reconnection mechanism is required to tear up the magnetic field. Recently, Buchner and Zelenyi showed that the chaotization of the electron motion can lead to fast collisionless reconnection in the Earth's magnetotail. In their theory, enhanced pitch angle diffusion is obtained when the curvature parameter κe decreases to κe ≃ 1.6. We apply Buchner and Zelenyi's theory to Jupiter's magnetosphere. The curvature parameter is obtained from the measured plasma parameters and from a self-consistent equilibrium model of the magnetic field, and the results for κe show that the larger the assumed plasma disc, the larger is the range where κe is less than or equal to the stochasticity threshold 1.6. This indicates that chaotic magnetic-field line reconnection may occur in Jupiter's nightside magnetosphere around 60RJ from the planet, and is consistent with thein situ magnetic-field observations, that show the signature of magnetic islands and of tearing-mode instability in the relevant region. We speculate that these processes, differently from the Earth's case, occur in a semi-steady way.