Double Layers: Kinetic Plasma Physics at the Venusian Bow Shock

Abstract:

The induced magnetosphere of Venus presents an obstacle to the solar wind. At the flow-obstacle interface, plasma is slowed, deflected, and heated. Based on observations of Earth's bow shock and magnetosheath, kinetic plasma processes are expected to play an important role in these dynamics at Venus. However, these processes have gone largely undetected at Venus due to the small number of measurements at sufficiently high sampling cadences. Using data from a Parker Solar Probe encounter with Venus, this study demonstrates the existence of kinetic-scale electric field structures, including plasma double layers, at the outer edge of the Venusian magnetosheath. Many of the double layers have signatures of developed two-stream instabilities and phase space holes. Double layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to the electron temperature change across the bow shock, consistent with double layers driven by mixing of inhomogeneous plasmas at the magnetosheath boundary. A large number of distinct double layers are found in few burst captures, implying that double layers, and the waves that they drive, have higher amplitudes relative to other high frequency bow shock and magnetosheath waves at Venus as compared to Earth. These are the first direct observations of plasma double layers beyond near-Earth space, demonstrating that kinetic plasma processes are active in diverse plasma environments, and can be identified when high cadence observations are available.