Impact of solar wind disappearance event on Martian nightside ionospheric species: First results

For the first time, we report the impact of a rarest solar wind phenomenon, i.e., disappearing solar wind (DSW) event on the Martian nightside ionosphere using MAVEN spacecraft datasets. During an extremely low solar wind density event, the nightside ionospheric densities particularly above 200 km, including electrons and ions (NO+, O2+, CO2+, C+, N+, O+, and OH+) experience significant enhancement at a fixed altitude. The electron and ion densities increase by a factor of ~2.5 and 10-67, respectively, compared to average quiet time. The increased plasma density, during DSW, suggests the expansion of the Martian ionosphere under extremely low solar wind dynamic pressure (~1.4 × 10⁻¹¹ Pa) contrasting with nightside ionospheric thermal pressure (>10⁻¹⁰ Pa). Further, the day-to-night plasma transport through cross-terminator magnetic topology may also be a contributing factor, causing the increased nightside ionospheric density. Therefore, this study sheds light on an unusual extreme state of the Mars-solar wind interaction.