Double Layers in the Martian Magnetosheath

The observation of electrostatic double layers in Martian magnetosheath plasma is reported, based on medium-frequency (100 Hz-32 kHz) electric field data recorded by the Langmuir Probe and Waves on board the Mars Atmosphere and Volatile Evolution spacecraft on 2021 January 1. A total of six burst mode events were scrutinized, revealing the occurrence of double layer structures. Overall, 79 double layers were identified, with their absolute amplitudes and widths found to be in the ranges of 0.4-3.3 mV m⁻¹ and 0.6-6.4 ms, respectively. The dominant frequency associated with the observed excitations lies well above the ion plasma frequency (f_pi). The identified structures were observed at 2600-4400 km altitude in the dusk sector (17-19 LT). Extensive analysis based on a nonlinear multifluid plasma model shows that the observed structures are electron-acoustic double layers. A comparison of theory and observations indicates that these double layers have spatial scales in the range of 0.4-10 km. This is the first detailed study to give conclusive evidence of the occurrence of double layers in the Martian plasma environment.