Origin, Variability, and Consequences of the Martian Aurora

Aurora have been observed at many solar system bodies, and provide a visual reminder of the coupling between flowing plasma, planetary magnetospheres, and atmospheres. While they are commonly associated with planets having global magnetic fields, auroral emission has also been reported at Venus and most recently near strong crustal magnetic fields at Mars. A global-scale magnetic field, then, seems not to be required for auroral emission, and it is an open question whether Earth-like auroral physics operate at Mars or Venus. In this presentation we will first review the observations of localized UV emission at Mars by Mars Express and supporting particle observations by Mars Global Surveyor and Mars Express. We will then discuss and evaluate the possible origins of the emission, including electrons stored in closed crustal magnetic fields, direct impact of the atmosphere by solar wind electrons via magnetic cusps, reimpact of ionospheric photoelectrons from the Martian dayside, and meteor impacts. We will discuss the implications of the discovery of aurora at Mars for plasma acceleration and escape on the night side, and for the creation of localized patches of night side ionosphere. Finally we will highlight outstanding questions and research directions related to Martian aurora for the coming years, including the requirements for observation of aurora at visible wavelengths at Mars.