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

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 (Z^ $hat{Z}$ 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 ±X^ $pm hat{X}$ 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 ±Y^ $pm hat{Y}$ directed. We additionally estimate that distortions in low altitude (<800 km) dayside draping along Z^ $hat{Z}$ 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.Plain Language SummaryMars presents a dynamic and complex obstacle to the solar wind, a supersonic flow of magnetized plasma from the Sun. This complexity is due to Mars’ ionized upper atmosphere, or ionosphere, and a patchwork of strong crustal magnetic fields that rotate with the planet. These factors perturb how the solar wind magnetic field drapes around Mars. The solar wind magnetic field is most often approximated as either eastward or westward directed as referenced by Mars’ longitude. For planets without internally generated magnetic fields like Venus it is expected that the solar wind magnetic field would drape symmetrically around the ionosphere. However, spacecraft measurements have revealed a more complicated draping pattern at Mars including northward and southward directed draping. We show that these alterations can be explained by combination of crustal magnetic fields at low altitudes and by a previously underestimated effect of induced magnetospheres at high altitudes. These dayside draping alterations propagate globally throughout the Mars system, potentially explaining previously observed alterations in expected magnetotail observations. We conclude with an updated guide for how solar wind magnetic field draping occurs around induced obstacles and suggest that this is a unifying phenomenon of planetary and solar wind interactions.Key PointsWe quantify Mars’ induced magnetic field response as compared to responses from the intrinsic crustal and direct solar wind magnetic fieldsWe expand induced magnetosphere theory after showing twisted dayside fields depend on an underestimated induced effect and crustal fieldsTwisted dayside draping is a precursor to, and aligns with, observations of the twisted magnetotail at Mars