Transient Foreshock Structures Upstream of Mars: Implications of the Small Martian Bow Shock

TL;DR

This paper investigates magnetic structures called foreshock bubbles upstream of Mars, revealing their formation mechanisms involving ion populations and magnetic field variations, which enhance understanding of Martian space weather phenomena.

Contribution

It provides the first detailed characterization of foreshock bubble structures at Mars and explains their formation involving specific ion populations and magnetic field dynamics.

Findings

Foreshock bubbles form at the upstream edge of moving foreshocks.

Ion populations include backstreaming and reflected ions contributing to structures.

Magnetic field and plasma density decrease inside foreshock bubbles.

Abstract

We characterize the nature of magnetic structures in the foreshock region of Mars associated with discontinuities in the solar wind. The structures form at the upstream edge of moving foreshocks caused by slow rotations in the interplanetary magnetic field (IMF). The solar wind plasma density and the IMF strength noticeably decrease inside the structures' core, and a compressional shock layer is present at their sunward side, making them consistent with foreshock bubbles (FBs). Ion populations responsible for these structures include backstreaming ions that only appear within the moving foreshock, and accelerated reflected ions from the quasi-perpendicular bow shock. Both ion populations accumulate near the upstream edge of the moving foreshock which facilitates FB formation. Reflected ions with hybrid trajectories that straddle between the quasi-perpendicular and quasi-parallel bow shocks during slow IMF rotations contribute to formation of foreshock transients.