Magnetic Field Draping in Induced Magnetospheres: Evidence from the MAVEN Mission to Mars

TL;DR

This study analyzes MAVEN magnetic field data to reveal altitude-dependent draping patterns in Mars' induced magnetosphere, highlighting the influence of IMF components and crustal fields on magnetospheric structure.

Contribution

It introduces a Bayesian regression model that accounts for IMF directions and crustal fields, refining the understanding of Mars' induced magnetosphere.

Findings

High-altitude draping is influenced by IMF components in the $ ext{±}oldsymbol{ extbf{X}}$ direction.

Low-altitude draping distortions are related to remanent crustal fields.

Outer tail morphology is governed by the induced response to IMF direction.

Abstract

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been orbiting Mars since 2014 and now has over 10,000 orbits which we use to characterize Mars' dynamic space environment. Through global field line tracing with MAVEN magnetic field data we find an altitude dependent draping morphology that differs from expectations of induced magnetospheres in the vertical ($\hat Z$ Mars Sun-state, MSO) direction. We quantify this difference from the classical picture of induced magnetospheres with a Bayesian multiple linear regression model to predict the draped field as a function of the upstream interplanetary magnetic field (IMF), remanent crustal fields, and a previously underestimated induced effect. From our model we conclude that unexpected twists in high altitude dayside draping ($>$800 km) are a result of the IMF component in the $\pm \hat X$ MSO direction. We propose that this is a natural outcome of current theories of induced magnetospheres but has been underestimated due to approximations of the IMF as solely $\pm \hat Y$ directed. We additionally estimate that distortions in low altitude ($<$800 km) dayside draping along $\hat Z$ are directly related to remanent crustal fields. We show dayside draping traces down tail and previously reported inner magnetotail twists are likely caused by the crustal field of Mars, while the outer tail morphology is governed by an induced response to the IMF direction. We conclude with an updated understanding of induced magnetospheres which details dayside draping for multiple directions of the incoming IMF and discuss the repercussions of this draping for magnetotail morphology.