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

The occurrence of Venusian lighting has been debated for decades. One key signature of lightning is the emission of whistler waves, which are electromagnetic plasma waves that propagate along magnetic field lines near the electron cyclotron frequency. Many whistler waves have been detected in Venus's ionosphere and induced magnetosphere, which have sometimes been interpreted as evidence for Venusian lightning. However, other signatures of lightning including optical flashes, are exceedingly rare. Multiple spacecraft, such as Cassini and Parker Solar Probe, have performed gravity assists at Venus and have not detected signatures of Venusian lightning in the broadband radio spectrum. These non-detections and rare optical flashes are consistent with extremely low rates of Venusian lightning. However, the Venusian lightning occurrence rates based on whistler wave observations are orders of magnitude greater than the occurrence rates based on other signatures of lightning. The inconsistency between these different signatures of lightning has sparked decades of debate on the possible existence and occurrence rates of lightning on Venus.