Escaping plasma structures in the Martian magnetotail as observed during two special MARSIS high-altitude campaigns

The nightside ionosphere of Mars is formed by plasma transport from the dayside and electron precipitation. Significant progress has been made in our understanding of its composition and structure at low altitudes, however, what happens at higher altitudes remains unclear. Plasma structures escaping from the nightside of Mars could reveal the plasma transport paths from the dayside and from the nightside to space. Furthermore, the response of escaping plasma structures to changing solar wind conditions will shed light on the dynamic evolution of the system. Mapping the paths of escaping plasma structures will result in a better understanding of the evolution of atmospheric escape at Mars and the contribution of escaping plasma structures to the total atmospheric loss. In this study we probe escaping plasma structures utilising two special campaigns of ESA's Mars Express mission as well as observations from NASA's MAVEN mission, in the high-altitude nightside ionosphere of Mars. Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is the radar on board Mars Express and it typically samples the ionosphere at altitudes no higher than ~1500 km. In our study we look at observations from consecutive orbits during two special MARSIS campaigns, each consisting of 5 orbits, that took place in September 2023 and April 2024, for which MARSIS was operated at altitudes up to 4000 km. We see a variable nightside ionosphere at high altitudes that changes between consecutive Mars Express orbits. MARSIS detects plasma structures, appearing at different altitudes or disappearing between orbits, although a consistent plasma presence in the terminator region is observed. We compare the observations from the special MARSIS campaigns with MAVEN measurements to better evaluate both the escaping plasma structures and the solar wind conditions. MAVEN too sees plasma structures at high altitudes on the nightside, changing between orbits, confirming the variability in the nightside ionosphere. Combining Mars Express and MAVEN data we further investigate the effect of changing solar wind conditions to the plasma structures.