Electric fields and waves in the Venus nightside magnetosphere

TL;DR

The Parker Solar Probe's first accurate electric field measurement in Venus's nightside magnetosphere revealed a predominantly electrostatic environment with minimal electromagnetic activity, indicating unique solar wind interactions with unmagnetized bodies.

Contribution

This study introduces a novel biasing technique for electric field measurements and provides the first detailed electric field data in Venus's nightside magnetosphere.

Findings

Minimal electromagnetic waves observed during nightside crossing

Presence of a few Hz electrostatic signals

Contrast with electromagnetic activity in sunlit regions

Abstract

On November 6, 2024, the Parker Solar Probe flew past Venus to make the first accurate electric field measurement in the nightside Venusian magnetosphere. To achieve this result, the electric field antennas were current biased in a way never before experienced by an electric field detector. This biasing requirement, that the positive bias current in the Venus shadow be about equal to the electron thermal current, is discussed and illustrated. About one minute of useful electric f ield data in the eight-minute nightside magnetosphere crossing was obtained, during which the only feature observed was a few Hz signal. This result, along with the magnetic field measurements, showed that there were few if any electromagnetic waves, such as low-frequency electromagnetic turbulence or whistlers, in the nightside crossing. Instead, a few Hertz, purely electrostatic signal was found. This suggests that the interaction of the solar wind with an unmagnetized body having an ionosphere may be different from that of previously studied magnetized bodies. In the sunlit flanks, many electromagnetic wave modes were observed. These results describe the first step in the proper technique for future measurements of electric fields in shadow.