Flows, Fields, and Forces in the Mars-Solar Wind Interaction

We utilize suprathermal ion and magnetic field measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, organized by the upstream magnetic field, to investigate the morphology and variability of flows, fields, and forces in the Mars-solar wind interaction. We employ a combination of case studies and statistical investigations to characterize the interaction in both quasi-parallel and quasi-perpendicular regions and under high and low solar wind Mach number conditions. For the first time, we include a detailed investigation of suprathermal ion temperature and anisotropy. We find that the observed magnetic fields and suprathermal ion moments in the magnetosheath, bow shock, and upstream regions have observable asymmetries controlled by the interplanetary magnetic field, with particularly large asymmetries found in the ion parallel temperature and anisotropy. The greatest temperature anisotropies occur in quasi-perpendicular regions of the magnetosheath and under low Mach number conditions. These results have implications for the growth and evolution of wave-particle instabilities and their role in energy transport and dissipation. We utilize the measured parameters to estimate the average ion pressure gradient, J x B, and v x B macroscopic force terms. The pressure gradient force maintains nearly cylindrical symmetry, while the J x B force has larger asymmetries and varies in magnitude in comparison to the pressure gradient force. The v x B force felt by newly produced planetary ions exceeds the other forces in magnitude in the magnetosheath and upstream regions for all solar wind conditions. Plain Language Summary The solar wind that flows out from the Sun and pervades our solar system is largely deflected around Mars by its interaction with the upper atmosphere. However, this interaction also transfers energy to planetary ions, giving some of them sufficient velocity to escape from Mars. Therefore, the Mars-solar wind interaction has implications for the long-term evolution of the Martian atmosphere and its habitability. In this work, we study the structure and variability of the interaction and the macroscopic forces responsible for decelerating and deflecting the solar wind around Mars as well as those that accelerate planetary ions. We also investigate the asymmetries in this interaction and how they change in response to variations in the incoming solar wind flow and the magnetic field carried with the flow.