Observations of Energized Electrons in the Martian Magnetosheath

TL;DR

This study reveals that electron energization in Mars's magnetosheath is more complex than previously thought, involving additional downstream acceleration that reduces expected asymmetries in electron distributions.

Contribution

It provides new observational evidence that electron acceleration occurs downstream of the bow shock, challenging the assumption of localized shock acceleration.

Findings

Electron energization is less asymmetric than expected.

Additional parallel acceleration occurs downstream of the bow shock.

Energization difference is at most 25% of predicted values.

Abstract

This observational study demonstrates that the magnitude and location of energization of electrons in the Martian magnetosheath is more complex than previous studies suggest. Electrons in Mars's magnetosheath originate in the solar wind and are accelerated by an electric field when they cross the bow shock. Assuming that this acceleration is localized solely to the shock, the field-aligned electron distributions in the sheath are expected to be highly asymmetric. However, such an asymmetry is not observed in this study. Based on the analysis here, it is suggested that an additional parallel acceleration takes place downstream of the Martian bow shock. This additional acceleration suppresses the expected asymmetry of the electron distribution. Consequently, along a flux tube in the magnetosheath that is tied on both ends to the bow shock the difference in energization between parallel and anti-parallel electrons is less than about 20 eV. Where this energization difference is expected to be maximal, we find the energization difference to be at most 25% of the predicted value.