Powerful lightning on Venus constrained by atmospheric NO

Abstract

Signs of lightning on Venus have long been sought, including by space missions and ground-based telescopes searching for optical flashes, plasma waves, or radio signatures. These efforts have yielded conflicting findings regarding the presence or absence of lightning in Venus's atmosphere. In this study we adopt an indirect approach to constrain the prevalence of lightning on Venus, using the chemical by-products it produces in Venus's atmosphere. Nitric oxide (NO) is a key tracer species of lightning, being exclusively generated by lightning in Venus's lower atmosphere. By calculating the present rate of atmospheric destruction of NO in Venus's atmosphere through photochemical-kinetic modelling, we constrain the lightning power required to sustain the estimated NO abundances on modern Venus. The reported NO constraints require lightning to generate at-least three times the power released on Earth; consistent with either a higher rate of strikes, or greater energy per strike, or a combination of both. Limited detections of optical flashes within the clouds could point to lightning striking deeper in the atmosphere and nearer the surface -- with the result that its optical flashes are obscured by the clouds -- driven by triboelectric charging during volcanic eruptions or wind interactions with surface sediments. Our findings underscore the importance for future missions of confirming lightning on Venus, either by verifying the below-cloud NO abundance, or by detecting another unambiguous lightning signature, to provide the first definitive evidence of lightning on a rocky planet other than Earth.