Transient Foreshock Structures Upstream of Mars: Implications of the Small Martian Bow Shock. Issue 8 (23rd April 2023)

• Record Type: Journal Article
• Authors: Madanian, H.; Omidi, N.; Sibeck, D. G.; Andersson, L.; Ramstad, R.; Xu, S.; Gruesbeck, J. R.; Schwartz, S. J.; Frahm, R. A.; Brain, D. A.; Kajdic, P.; Eparvier, F. G.; Mitchell, D. L.; Curry, S. M.
• Is Part Of: Geophysical research letters. Volume 50:Issue 8(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-23
• Subjects: shocks -- solar wind -- space plasmas -- Mars; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL101734
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The typical subsolar stand‐off distance of Mars' bow shock is of the order of a solar wind ion convective gyroradius, making it highly non‐planar to incident ions. Using spacecraft observations and a test particle model, we illustrate the impact of the bow shock curvature on transient structures which form near the upstream edge of moving foreshocks caused by slow rotations in the interplanetary magnetic field (IMF). The structures exhibit noticeable decrease in the solar wind plasma density and the IMF strength within their core, are accompanied by a compressional shock layer, and are consistent with foreshock bubbles (FBs). Ion populations responsible for these structures include backstreaming ions that only appear within the moving foreshock and reflected ions with hybrid trajectories that straddle between the quasi‐perpendicular and quasi‐parallel bow shocks during slow IMF rotations. Both ion populations accumulate near the upstream edge of the moving foreshock which facilitates FB formation. Plain Language Summary: Planets in the solar system are continuously impacted by the solar wind, a plasma flow originating at the Sun and propagating through the interplanetary medium at high speeds. The solar wind also carries a magnetic field which at times contains twists or discontinuities. The discontinuities are associated with large scale electric currents that can have planar shapes. A planetary obstacle significantly modulate the solar wind plasma and the interaction of solar wind discontinuities with the modulated plasma upstream of the planet leads to formation of transient structures. Due to their relatively large size, these structures can significantly impact and destabilize plasma boundaries at lower altitudes closer to the surface. The results of this paper improve our understanding of solar wind interactions and formation of transient structures upstream of Mars. Key Points: Foreshock bubbles can form upstream of Mars Slow field rotations can cause foreshock bubbles while reflected ions from the quasi‐perpendicular bow shock contribute to their formation Unique ion kinetic scale processes exist around foreshock structures at Mars due to the different interaction size scale