IMF Control of Electron Aurora Across Mars' Crustal Magnetic Fields: Insights Into Electron Sources

Abstract

We investigate Martian electron aurora utilizing 130.4 nm auroral observations from the Emirates Mars Ultraviolet Spectrograph and IMF clock angle measurements and estimates from MAVEN. Analysis reveals that more than 5 R aurora occurrence in a given region can vary by up to a factor of seven with IMF orientation, generally highest for southward IMF and lowest for westward IMF, with higher auroral occurrence post-dusk, decreasing toward and past midnight before increasing again toward dawn. A broad diversity of IMF and local time dependence of aurora occurrence is observed across Mars' crustal magnetic fields. The polarity of a given crustal field determines whether its field lines preferentially magnetically connect to dayside ionospheric or nightside magnetotail electron sources in the post-dusk or pre-dawn sectors. We thus establish a “source preference metric”, that is, the excess likelihood of aurora when likely magnetically connected to the nightside versus dayside. A wide range of source preferences are observed across the crustal field features, with some showing higher occurrence for night sources, day sources, or neither, often differently when in the post-dusk or pre-dawn sectors. A generally stronger nightside source preference is found for radially inward crustal fields in the predawn sector, and for weaker outward crustal fields in the post-dusk sector. These results highlight the complex and dynamic nature of Mars' magnetic topology in controlling auroral electron access. Future studies integrating in situ electron measurements with synoptic and limb auroral imaging will further constrain the relative contributions of dayside and magnetotail electron populations to Mars' auroral processes.