Mars Discrete Aurora: A Comprehensive Survey for Detection & Characterization by MAVEN/IUVS

We present the results of a comprehensive search for discrete aurora emissions on Mars from
six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a
localized and transient form of aurora apparently unique to Mars, owing to its lack of a global
magnetic Teld. The auroral emissions originate from precipitating electrons accelerated by the
reconTguration of Mars' crustal magnetic Telds as the planet rotates relative to the external
magnetic Teld carried by the solar wind. This process is distinct from other more widespread
diffuse and proton aurora also seen at Mars.
Discrete aurora was discovered in regions of strong crustal magnetic Telds by the SPICAM
instrument on Mars Express using limb scanning [Bertaux et al., 2005]. The emission
appeared in patches ~tens of km across at altitudes ~130 km. Further analysis revealed a
total of 20 instances of auroral patches during 10 years of intermittent SPICAM observations
[Gérard et al., 2015]. Auroral excitation was attributed to the precipitation of electrons,
typically ~100 eV - 1 keV. MAVEN/IUVS obtained the Trst images of the phenomenon
(Schneider et al. 2018).
We have examined MAVEN's mission-long dataset of nightside limb scans spanning more
than 10,000 orbits over nearly 6 Earth years. Events were identiTed by signiTcant emission in
the CO Cameron bands (190-270 nm) and were individually conTrmed to be free of stray light
and cosmic ray interference. More than 500 discrete aurora events were detected, increasing
the number of known events by more than an order of magnitude. The Tgure shows a
remarkable string of distinct events seen during a single 20-minute passage of Mars' crustal
Teld region. The observed events show a strong concentration near crustal Telds in the south,
but also exhibit a substantial distribution spread more uniformly over the entire planet. Some
events are seen at the tangent altitude expected for electron precipitation, but many appear at
lower projected altitudes. We infer these are small patches of emission in front of (or behind)
the limb itself, and in some cases the spacecraft was probably imbedded in the emission.
See also the related abstract by Soret et al., this conference,