Non-Lightning-Generated Whistler Waves in Near-Venus Space

Abstract

The occurrence of Venusian lighting has been debated for decades. Terrestrial lightning generates whistler waves, and many whistlers have been observed in Venus's ionosphere and induced magnetosphere. Venusian lightning occurrence rates derived from these whistler observations are relatively high. However, optical flashes on Venus are exceedingly rare and Venus encounters by multiple spacecrafts have not detected lightning. These non-detections and rare optical observations are consistent with low Venusian lightning occurrence rates, which is incompatible with the high whistler-derived rates. We present observations of whistlers during a Parker Solar Probe Venus gravity assist and eliminate lightning as a possible source. These waves are observed at an altitude of 0.39 Venus radii on Venus' nightside with planetward propagation and are simultaneous with Langmuir waves. This provides a mechanism for whistler generation near Venus that does not require lightning, and suggests that whistler-based lightning occurrence rates may be overestimated.