Aurorae are known to occur on many planets and moons in our solar system. However, with the debatable exceptions of Venus and Titan, only bodies with intrinsic global magnetic fields have been found to have aurorae. Mars has no global magnetic field, though it does possess strong localized crustal magnetic fields, and it is unclear whether we can expect to observe auroral processes at Mars. Regardless of expectations, however, a recent observation of UV emission above strong crustal magnetic sources on the Martian night side by Mars Express (MEX) provides evidence that something like terrestrial auroral processes may also operate at Mars.

I will present Mars Global Surveyor (MGS) observations of thousands of peaked electron spectra, and describe their geographical distribution and the influence of seasonal and solar wind variation on their distribution and appearance. The peaked spectra are primarily associated with regions of strong crustal fields and are very reminiscent of terrestrial auroral spectra measured by FAST, suggesting the existence of an acceleration mechanism or mechanisms analogous to those which operate in the terrestrial auroral zone. These electron measurements, the most energetic of which are capable of producing the emission observed by MEX, therefore provide additional support for the existence of Earth-like auroral physics at Mars. The detailed topology of the interaction is likely to be much more complex and variable than that at Earth, however, as localized crustal magnetic field regions rotate into and out of the solar wind, causing significant reconfigurations of magnetic topology on hourly timescales, and making it difficult to imagine a system of currents analogous to that in the terrestrial magnetosphere. We are far from understanding the Mars-solar wind interaction, but have begun to catch enough glimpses of it to see how unique it must be.