Sinuous Aurora at Mars: exploring a new phenomenon with data and models
Journal Article
Overview
abstract
Benefiting from a large orbit and high sensitivity, the Emirates Mars mission EMUS instrument has provided the first opportunity to regularly image Mars’ discrete FUV aurora synoptically.  EMUS has collected nearly 1000 synoptic observations of the Mars nightside have revealed at least three distinct types of discrete Aurora: 1) crustal field aurora, appearing in regions of mostly radial crustal magnetic fields, 2) patchy discrete aurora, observed away from strong crustal fields, and 3) sinuous discrete aurora, extending from the terminator typically thousands of kilometers onto the nightside, away from crustal fields.Sinuous Discrete Aurora (SDA) is observed in approximately 5% of observations and is characterized by 2 primary attributes: morphology and the local time of its intersection with the terminator. Morphologies include serpentine, approximately linear, and short/lumpy. Dusk-side SDA does not occur preferentially for any particular interplanetary magnetic field (IMF) orientation, while Dawn and Midnight SDA appear to show a preference for northeastward IMF directions measured in situ by the MAVEN spacecraft. Dusk SDA observed about twice as often as Dawn or Midnight SDA. SDA reflect conditions whereby particular magnetic topologies connect the nightside atmosphere to a source of abundant electrons, whether dayside photoelectrons or sufficiently energetic magnetotail/sheath electrons.  In particular, midnight sinuous discrete aurora appear to be a projection of the tail current sheet, a persistent but highly variable feature of Mars’ double-lobed magnetotail resulting from the draping of the IMF around the conducting obstacle of Mars’ dayside ionosphere.  This interpretation is supported by magnetohydrodynamic (MHD) simulations, showing that the orientation of the tail current sheet approximately matches the orientation of midnight SDA.EMM EMUS promises to be an invaluable tool in helping to understand the drivers of Martian Aurora.
