MAVEN’s Imaging UltraViolet Spectrograph (IUVS) has identified and characterized three fundamentally different types of aurora on Mars, each profoundly different from comparable types on Earth and other planets. These differences stem from Mars’ lack of a global magnetic field and presence of localized crustal magnetic fields. Two types of auroral emission have been detected on Mars’ nightside caused by different populations of precipitating charged particles. The first type, discrete aurora, are localized near the boundary between open and closed crustal magnetic field lines. They recur in evening hours when the inter-planetary magnetic field is favorable. IUVS discovered a second type, diffuse aurora, which are widespread and potentially global. They are triggered by relativistic electrons or protons from the Sun. IUVS also discovered a third type, proton aurora, on Mars’ dayside as excess hydrogen Lyman alpha emission confined to Mars’ thermosphere. Proton aurora are enhanced in southern summer, when dust storms enhance hydrogen escape.
IUVS results dispel common misconceptions that aurora only occur on magnetized planets near the edges of closed field lines. In this sense, Mars may serve as the best archetype for auroral processes on unmagnetized planets in our solar system and beyond.