First Synoptic Images of FUV Discrete Aurora and Discovery of Sinuous Aurora at Mars by EMM EMUS

We present the first measurements of Mars discrete aurora in the extreme ultraviolet (75% of nightside images, with patterns shifting visibly over 15–20 min. Aurora is observed most frequently in regions of open magnetic topology (where crustal magnetic fields are very weak and/or vertical), with the brightest aurora where crustal fields are strongest. We present the first disk‐averaged spectrum of discrete aurora, with several O, C, and CO features as expected for electron impact primarily on CO2. We categorize discrete auroral morphology into three types: crustal field aurora, non‐crustal field patchy aurora, and a new type we call “sinuous” aurora, an elongated serpentine structure that stretches thousands of kilometers into the nightside from near midnight in the northern hemisphere. These observations point to a highly dynamic environment in Mars' magnetotail. Plain Language Summary In this study, we present near‐global images of localized aurora on Mars and the first measurements of these aurora at very short ultraviolet wavelengths (75% of images, with their patterns shifting visibly over 15–20 min. They are observed most frequently in regions where magnetic fields are very weak or both strong and vertical, with the brightest aurora where magnetic fields are strongest. We present the first disk‐averaged spectrum of these auroras, showing features expected for electrons striking CO2 (the most abundant gas in Mars’ atmosphere). We categorize discrete auroral patterns into three types: those near strong vertical crustal magnetic field, patchy aurora near very weak crustal fields, and a new type we call “sinuous,” an elongated serpentine structure that stretches thousands of kilometers into the nightside from near midnight in the northern hemisphere. These observations point to a highly dynamic environment in Mars’ nightside space environment. Key Points We present the first disk measurements of Mars discrete aurora in the EUV end FUV, with the oxygen feature at 130.4 nm being the brightest Auroras are detected in ∼75% of nightside images and are more likely where crustal fields are either very weak or both strong and vertical An elongated, sinuous discrete aurora is discovered, extending far into the nightside. It