Logo image
Back
MAVEN Observations of the Martian Magnetospheric Response to Simultaneous Quasi‐Radial Interplanetary Magnetic Field and Low Dynamic Pressure
Journal article   Open access   Peer reviewed

MAVEN Observations of the Martian Magnetospheric Response to Simultaneous Quasi‐Radial Interplanetary Magnetic Field and Low Dynamic Pressure

K. G. Hanley, S. Xu, C. M. Fowler, C. Mazelle, D. L. Mitchell, J. P. McFadden, J. S. Halekas, L. Andersson, J. Espley and S. M. Curry
Journal of geophysical research : Space physics (2013 - Present), Vol.131(4), e2026JA035312
04/2026
DOI: 10.1029/2026JA035312
url
https://doi.org/10.1029/2026JA035312View
Published (Version of record) Open Access

Abstract

The state of Mars' induced magnetosphere is highly dependent on upstream solar wind conditions. Changes in dynamic pressure alter the locations of magnetospheric boundaries such as the bow shock and induced magnetosphere boundary, while the orientation of the interplanetary magnetic field (IMF) impacts the formation of the bow shock. We present Mars Atmosphere and Volatile EvolutioN observations from a period when the solar wind dynamic pressure was low and the IMF was nearly radial. The quasi‐radial IMF appeared to prevent the formation of the usual quasi‐perpendicular bow shock, instead producing a spatially extended quasi‐parallel shock in the observed region. The ambipolar potential in the magnetosheath/shock region enabled planetary heavy ions to leak through the shock and flow upstream. These ions were first accelerated by the solar wind motional electric field, which remained an important ion energization mechanism even though the solar wind flow and IMF were roughly aligned throughout most of the system. The ionosphere had expanded out to very high altitudes as the result of low dynamic pressure. The ionosphere was also unmagnetized, perhaps because of the formation of an ionopause‐like boundary. Finally, we compare two adjacent orbits and suggest that Mars' remanent crustal fields may fundamentally alter bow shock formation during radial IMF conditions. Studying unusual combinations of solar wind conditions like the case presented here is critical for understanding the fundamental physics driving induced magnetospheres. Plain Language Summary Because Mars lacks an intrinsic magnetic field, the state of its plasma environment is determined by upstream solar wind conditions. We present observations from a period of unusual upstream conditions, when the pressure of the solar wind impacting the planet was very low and the interplanetary magnetic field (IMF) pointed toward the planet. The low pressure allowed Mars' ionosphere to expand out to higher altitudes than usual. The magnetic field direction changed the physics acting in the system, leading to a spatially extended, highly variable planetary bow shock rather than the typical sharp boundary. Heavy ions from the ionosphere flowed sunward because of an electric field across the shock region. The IMF was shielded out of the ionosphere. Studying unusual events like the one presented here is critical for understanding the fundamental physics driving induced magnetospheres. Key Points The motional electric field strongly contributes to planetary ion energization, even when the interplanetary magnetic field (IMF) is quasi‐radial The ambipolar electric field enables the leakage of planetary heavy ions into the upstream region during quasi‐radial IMF The location of the strongest crustal fields may fundamentally alter the solar wind‐magnetosphere interaction during quasi‐radial IMF
 ambipolar field Mars MAVEN motional electric field radial IMF

Details

Metrics

1 Record Views
Logo image