The polar ionosphere of Mars as seen by Mars Express-MARSIS during a full solar cycle

Since Mars does not have a global intrinsic magnetic field, the variability of Mars polar ionosphere is due mainly to the solar irradiance flux and neutral atmospheric variations. Although for almost half of a Martian year each polar cap is in near darkness, the ionosphere is still present (although weak) mainly maintained by dayside transport and electron precipitation. Therefore, ionospheric dynamics of this region may be more important than previously anticipated. This is especially significant in the southern hemisphere where the presence of intense crustal magnetic fields and how they reconnect with the solar wind play a large role into ionospheric dynamics. In this study, we take advantage of the large exploration of both polar caps by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on board Mars Express and we present its polar ionospheric observations during the complete lifetime of MARSIS, which covers a bit longer than a full solar cycle. We also evaluate the response of the polar ionosphere to the presence of crustal magnetic fields, as well as the effect of seasons and the solar cycle.