Study of Martian Ionospheric Plasma Depletion Events using MAVEN and Mars Express Spacecraft

Plasma Depletion Events (PDEs), characterized by a significant reduction (at least tenfold) in ion number density, are known to occur in the Martian ionosphere. Since its launch in September 2014, the MAVEN spacecraft has spotted around 1000 PDEs, primarily located in the nightside ionosphere and regions with strong crustal magnetic fields. We show that dayside PDEs are associated with an increased level of electrostatic fluctuations and suggest their formation through ambipolar diffusion triggered by the sudden escape of suprathermal electrons. We further investigate possible concurrent detections of PDEs by MAVEN and Mars Express. For this purpose, local electron density measurements from Mars Express near the MAVEN-identified PDEs are systematically checked. We present the first multi-spacecraft observations of PDEs, and we use them to discuss their spatio-temporal extents.