Electron Bulk Heating at Saturn's Magnetopause

Abstract

The magnetopause (MP) is the natural boundary of a planetary magnetosphere. It is formed by the interaction between the solar wind and planetary magnetosphere. At Saturn, it separates the magnetospheric magnetic field and plasma (mainly from the moon Enceladus) from the interplanetary magnetic field (IMF) and solar wind plasma that has to flow around the magnetospheric obstacle (Baines et al., 2018). Cassini observations of magnetic field and plasma have also revealed that the disk-like magnetosphere imposes an "inflation" of the magnetopause at near-equatorial latitudes (Pilkington et al., 2014).Magnetic reconnection is an important process at this boundary as it can energize plasma via the release of magnetic energy when the fields undergo a topological change to a lower energy state (Øieroset et al., 2001). The signature of this process is heated high speed plasma jets (Yamada et al., 2010). Direct evidence of magnetic reconnection signatures has been observed at Saturn's magnetopause. For example, McAndrews et al. (2008) reported two magnetopause crossings with heating in the electrons and ions along field lines just outside the magnetopause that is highly suggestive of energization comparable to that associated with the reconnection process at Earth.

Automated bow shock and magnetopause boundary detection with Cassini using threshold and deep learning methods

“…They showed that the weaker the B-gradient, the higher the energy of electrons is required to escape into the magnetosheath: E.g., for a magnetic field gradient scale length of ~17 R E along the magnetopause, the minimum kinetic energy for loss is ~3 MeV. The large variety of MP crossings is likely due to the different plasma processes and evolving structures which may occur at the MP boundary such as electron heating associated with magnetic reconnection (McAndrews et al, 2008;Cheng et al, 2021), Kelvin-Helmholtz vortices, (Masters et al, 2010), plasma depletion layers (Masters et al, 2014) and low-latitude boundary layers (Masters et al, 2011).…”