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 ∼100 ms and several kilometers, respectively. The results thus suggest that the waves may play an important role in the interaction region. Plain Language Summary: Unlike Earth, Mars does not have a global dipole magnetic field to protect its upper atmosphere against the solar wind. In the absence of this magnetic shield, charged particles originating from the Sun stream through the Martian upper atmosphere and strip away a small fraction of ions from its ionosphere. The relative importance of various mechanisms that lead to the transfer of energy and momentum from the flowing solar wind to the Martian ions is not fully understood. Here, we present data obtained by NASA's MAVEN spacecraft that shows that the interaction region of the solar wind and the Martian plasma environment features intense plasma waves. Simulations suggest that the electric fields of these waves can efficiently couple the charged particles from the solar wind with those from the Martian ionosphere and facilitate the exchange of energy and momentum. Key Points: Plasma waves in the frequency range of ion acoustic and lower‐hybrid frequencies are often observed along with accelerated planetary ionsThe turbulence region features ion phase‐space holes and double layers that likely evolve from waves in the ion acoustic frequency rangeWave structures are very effective in coupling the flowing solar wind and the Martian plasma [ABSTRACT FROM AUTHOR]