Entering the "magnetic highway": energetic particle anisotropies at the heliospheric boundary

TL;DR

This paper investigates how energetic particles cross into the heliospheric boundary region called the 'magnetic highway', revealing the formation of a loss-cone distribution due to low pitch-angle scattering.

Contribution

It provides a kinetic model explaining the particle distribution transition at the heliospheric boundary, highlighting the role of low pitch-angle scattering.

Findings

Particle distributions peak at 90° pitch angle before disappearance.

A loss-cone distribution naturally forms at the boundary.

Low pitch-angle scattering rate facilitates particle escape.

Abstract

In August of 2012 the Voyager 1 space probe entered a distinctly new region of space characterized by a virtual absence of heliospheric energetic charged particles and magnetic fluctuations, dubbed a "magnetic highway". Prior to their disappearance, the particle distributions strongly peaked at a 90$^\circ$ pitch angle implying a faster particle escape along the magnetic field lines. We investigate the process of particle crossing from the heliosheath region into the "magnetic highway" region using a kinetic approach resolving scales of the particle's cyclotron radius and smaller. We show that a "loss-cone" type distribution naturally arises as the orbiting particles enter a region of space with an extremely low pitch-angle scattering rate.