Martian Nightside Aurora Observed by MAVEN Remote and In-Situ Instruments

Since NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) arrival at Mars on 22^ndSeptember 2014, MAVEN's Imaging Ultraviolet Spectrograph (IUVS) has detected the localized emission of aurora from limb observations of the nightside atmosphere on a total of 27 orbits. MAVEN is first to place the detection of aurora from the nightside of Mars in context with contemporaneous particle and magnetic field measurements from MAVEN's Particle and Fields Package (PFP). MAVEN also provides measurements close to the altitude range aurora is expected to occur at Mars, between 110 km - 160 km. This study demonstrates an association between localized Martian aurora and patches of electrons in the optical shadow of Mars between altitudes of 130 km - 300 km. The electron signatures occur with a range of field aligned (toward Mars) electron energy spectra and magnetic field orientation (radial to horizontal). That is, energy spectra displaying ionospheric-like electrons to energy spectra displaying solar wind-like electrons are observed. Also, the electron patches can occur with accelerated electrons, as well as electrons that show no acceleration. Electron patches observed with accelerated electrons, can occur as part of an "inverted-V" electron energy-time structure or as part of an electron energy dispersion feature. Periods of accelerated electrons are reported that accompany large electric field wave amplitudes up to 100 mV/m. Unusual spectral features are presented where accelerated electrons are observed alongside additional peaks in the electron energy flux close to photoelectron energies or the sharp drop-off in the electron energy flux below photoelectron energies. Such features are interpreted to result from magnetic field lines that extend beyond the optical shadow of Mars, where electrons from either or both the dayside ionosphere and the solar wind are accelerated towards the nightside atmosphere of Mars. A number of IUVS auroral observations with large distances to the tangent point were found to repeat in the strong crustal magnetic fields. Intervening MAVEN orbits crossing the line of sight locations showed an association with depressions in the crustal magnetic field strength, possibly due to field aligned currents. Such signatures are investigated for a possible relationship to IUVS auroral observations.