Abstract
The Martian ionosphere contains intriguing structures known as Plasma Depletion Events (PDEs). These events are characterized by ion densities significantly lower than the background, typically by more than an order of magnitude.
Although the solar zenith angle and crustal magnetic fields influence the occurrences of PDEs, no significant changes in the magnetic field occur during these events. PDEs typically take place above 250 km on the dayside and below 250 km on the nightside of Mars.
However, despite their prevalence, the cause of these events remains elusive. In this study, we investigate a formation mechanism of dayside PDEs based on the analysis of nearly 400 events identified in the Mars Atmospheric and Volatile Evolution (MAVEN) spacecraft data.
We demonstrate that both the electron temperatures and electric field wave power increase during the events. Additionally, the events are associated with energetic electrons at more field-aligned pitch angles and energetic lighter ions.
We suggest that these energetic particles heat the plasma within the depletion region, possibly through electrostatic turbulence, resulting in ambipolar diffusion and the eventual escape of plasma from the heated region.