EMM EMUS Observations of Martian nightside discrete EUV and FUV Aurora

<p>Here we report on synoptic (or &#8220;disk&#8221;) observations of Martian discrete aurora in the extreme and far ultraviolet (<200 nm), made by the Emirates Mars Ultraviolet Spectrometer (EMUS) on board the Emirates Mars Mission (EMM). EMM is well-suited to studying aurora due to its high altitude vantage point and regular observation cadence and the high sensitivity of the EMUS instrument.&#160; The first EUV/EUV auroral spectra measured at Mars reveal O, C, and CO features from 99 to 165 nm. Auroral detection increases with solar activity and discrete aurorae display significant variability over ~20 minute timescales.&#160; Three distinct types of discrete aurora have been identified based on these images. &#160;The first type appears where Mars&#8217; crustal magnetic fields are both strong and vertical and are consistent with point detections made by both Mars Express and MAVEN. The second appears in coherent patches away from crustal magnetic fields and is generally weak. The third is a new phenomenon, which we have named &#8220;sinuous discrete aurora&#8221; due to its serpentine shape, typically extending from the terminator thousands of kilometers into the nightside. &#160;Investigation into its causes is ongoing but it likely reflects the morphology of Mars&#8217; magnetotail current sheet. &#160;Joint analysis of discrete aurora with EMM, MAVEN, and Mars Express promises to elucidate the processes driving the aurora on Mars.</p>