Limb and Nadir observations of Discrete Aurora on Mars: Insights into auroral triggering

MAVEN’s Imaging Ultraviolet Spectrograph has identified nearly 500 occurrences of discrete aurora events on Mars, which are patchy, sporadic ultraviolet emissions emanating from the upper atmosphere. We confirm prior results finding that emissions are highly correlated with crustal magnetic fields results, with the brightest and most frequent occurrences located around strong crustal fields in the southern hemisphere. The larger dataset shows that events can also occur globally, in regions of weak or absent crustal fields. Recently analyzed nadir observations provide improved localization of events and broader simultaneous geographic and local time coverage. We find that events occur primarily in evening hours, especially during favorable orientations of the interplanetary magnetic field. Under these conditions, auroral events probably occur nightly and last for hours. We have also identified specific regions that are triggered after midnight, and will discuss possible explanations based on their magnetic configuration.