Aurora in Martian Mini Magnetospheres

Auroral processes are active at Mars, which lacks a global dynamo field. Observations of relatively faint UV emission in crustal magnetic fields demonstrate that upper atmospheric species are excited in cusp regions, presumably by incident particles directed along cusp flux tubes. Measurement of particles and fields above the crustal fields, including counterstreaming energized ion and electron populations, suggest that electrons are accelerated downward into the atmosphere, at least partly by a quasi-static field-aligned potential. A variety of additional mechanisms may be contributing to aurora, including day-night transport of ionospheric particles, waves and reconnection, and particle acceleration in the magnetotail current sheet. Future observations and modeling should help to distinguish between the different mechanisms, constrain the variation in auroral acceleration and brightness at different wavelengths, correlate auroral activity with external conditions, and determine the importance of auroral processes for upper atmospheric electrodynamics and atmospheric escape.