MAVEN observations of large scale magnetic depletions in the Martian ionosphere

Small scale current sheets have been observed in the Martian ionosphere by multiple spacecraft, including the Mars Global Surveyor (MGS) and Mars Atmosphere and Volatile EvolutioN (MAVEN) missions. These current sheets are characterized by relatively small (~a few nT) reductions in the magnetic field strength and rotations in the magnetic field vector, over spatial scales of a few kilometers. These current sheets are typically associated with crossing the magnetotail current sheet on the nightside of the planet, or as signatures of solar wind current sheets being convected through the ionosphere by the flowing solar wind, when on the dayside of the planet. Recently, the MAVEN spacecraft has observed features demonstrating similar characteristics to these small scale current sheets, but at much larger spatial scales, spanning hundreds of kilometers in some cases. The magnetic field strength reduces to close to zero in many cases. Such events occur less frequently than the previously studied small scale current sheets, and the origin of these large scale magnetic depletions is not yet known. We will present the statistical characteristics of these large scale magnetic depletions in the ionosphere, and discuss their possible formation mechanisms, including the convection of solar wind current sheets within the ionosphere, and the flowing of ionospheric currents that aid in standing off the impinging solar wind.