Meteors Might Masquerade as Lightning in the Atmosphere of Venus.

Introduction: The Akatsuki mission's Lightning and Airglow Camera (LAC) can detect lightning flashes with a filter centered on the emission lines of oxygen (OI) near 777 nm. In 22 hours of observation over 4 years, Akatsuki only observed one optical flash (Takahashi et al. 2021). Some scientists attributed this flash to lightning because a meteor fireball bright enough to produce this flash—if assumed to emit as a blackbody—was statistically improbable. However, the emission spectra of small meteors are not always blackbodies. We seek to determine if meteors are more likely than lightning to produce optical flashes in Venus's atmosphere. Overall, our study has implications for understanding the atmospheric and geologic activity of Venus—and to engineering new in situ missions.

Methods and Results: We developed a Monte Carlo model to generate the production function for optical flashes from meteor fireballs in the atmosphere of Venus. For example, a statistically common meteor with a mass of ~2 kg and entry velocity of ~25 km/s could produce ~107 J of optical energy in the LAC filter (as observed) if ~7% of its initial kinetic energy is converted to optical energy and ~25% of the total optical energy is emitted by atmospheric oxygen. Atmospheric emission provided ~30% of the total optical energy in the fireball of a ~1 kg Geminid meteor at Earth, including ~7% in the LAC filter – 10x more than predicted by a blackbody (Madiedo et al. 2013). We use a Markov chain Monte Carlo model to compute the probability of observing a single optical flash from an ablating meteor with LAC (and other flashes with ground-based telescopes).

Conclusions: Meteors in the atmosphere of Venus can produce detectable optical flashes. Lightning may be rare or even nonexistent in the clouds of Venus—if so, lightning would not be a hazard to proposed missions with a long-lived aerial platform in the clouds (e.g., Byrne et al. 2022). Instead, volcanic and/or eolian activity could generate lightning near the surface, which could explain observed whistler-mode waves (Hart et al. 2022), signaling that Venus is geologically active today. Ultimately, lightning illuminates the power of studying Venus as a planetary system.