Micro-Scale Plasma Instabilities in the Interaction Region of the Solar Wind and the Martian Upper Atmosphere

We present results, obtained by several instruments onboard NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, that show that the interaction region of the solar wind and the Martian upper atmosphere coincides with intense plasma wave activity. The turbulence region features nonlinear structures, identified as ion phase-space holes and double layers, that emerge in the saturation phase of instabilities in the ion-acoustic frequency range. One-dimensional particle-in-cell simulations suggest that the waves and the nonlinear structures are very effective in coupling the flowing solar wind and the Martian plasma. Specifically, the simulations show that the magnetic field-aligned component of the solar wind protons decelerates by about 20% in temporal and spatial scales of the orders of similar to 100 ms and several kilometers, respectively. The results thus suggest that the waves may play an important role in the interaction region.