The Transient Topside Layer and Associated Current Sheet in the Ionosphere of Mars

Radar soundings from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on board the Mars Express spacecraft have shown that transient layers exist in the dayside upper ionosphere of Mars. The most prominent of these features is a second layer at an altitude near 200 km, well above that of the main photoionization layer. While the general properties of this layer have been studied previously, the inner workings of this layer, and the mechanisms that drive it, are only now becoming clear. With the addition of solar wind, particle, and magnetic field instruments carried by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, a more detailed analysis has now been completed. Results show the existence of local current sheets in the upper Martian ionosphere in conjunction with the appearance of the second layer. These currents reveal an important magnetic aspect to the transient layer and point to a variety of possible explanations for its formation, including the Kelvin-Helmholtz instability, magnetic flux ropes, x-type magnetic reconnection, and solar wind magnetic field rotations.