# Electric Fields and Waves in the Venus Nightside Magnetosphere

## TL;DR

The Parker Solar Probe measured electric fields on Venus's nightside, revealing low-frequency electrostatic signals instead of expected electromagnetic waves.

## Contribution

The study introduces a new method for biasing electric field antennas in the Sun's shadow and observes unique electrostatic turbulence on Venus's nightside.

## Key findings

- Low-frequency electrostatic turbulence was observed in Venus's nightside magnetosphere.
- Few or no electromagnetic waves were detected in the nightside crossing.
- An improved algorithm for biasing electric field antennas was developed.

## 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 at Venus. 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 field 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. An additional result of this research is development of an improved algorithm for biasing electric field antennas in the Sun’s shadow which improves on guessing the bias current as done in this research.

The electric field instrument on the Parker Solar Probe had a bias current that was varied while the spacecraft was in the Venusian nightside magnetosphere, such that there were times when the bias current was appropriate for an accurate measurement of the electric field. Low frequency electrostatic turbulence was observed and no electromagnetic waves, such as whistlers, were seen.