Numerical simulations of TLE generation in the Jovian atmosphere

Since the 1953 Urey–Miller experiments, which produced organic precursors through electrical discharges in a simulated primordial Earth, electrical activity has been recognized as crucial for atmospheric evolution. Understanding planetary lightning, therefore, becomes essential when searching for life indicators across planets. Lightning activity has been confirmed through optical observations on Jupiter and Saturn, inferred electromagnetically on Uranus and Neptune, and theoretically predicted for Venus, Mars, and Titan. However, direct lightning detection faces significant challenges. Lightning typically originates in deep convective clouds, often below visible cloud layers where photons are heavily absorbed. This obscuration complicates direct optical detection from space. An alternative approach is to infer lighting by detecting transient luminous events (TLEs; sprites, jets, and Elves) which manifest in the upper atmosphere and produce distinctive optical and chemical signatures potentially more accessible to remote observation. Theoretical considerations based on a simple 1D quasi-electrostatic model (Yair et al., 2009; https://doi.org/10.1029/2008JE003311) predicted the possible occurrence of sprites on Jupiter, presuming that lightning discharges behave as on Earth (Kolamšová et al., 2023; https://doi.org/10.1038/s41467-023-38351-6). Recently, Giles et al. (2020; https://doi.org/10.1029/2020JE006659) reported the detection of unusual optical emissions in Juno images of Jupiter. Eleven bright transient flashes were observed by the spacecraft's UV instrument, with an average duration of 1.4 ms. They were located 260 km above the 1-bar level of Jupiter's atmosphere and were dominated by H₂ emission. These observations are consistent with TLEs (possibly Elves). We present results from a three-dimensional quasi-electrostatic model of TLE generation developed by Haspel et al. (2022; https://doi.org/10.1016/j.jastp.2022.105853), which has been adapted to the Jovian atmospheric conditions for this study. The simulations investigate TLE inception volumes across different cloud configurations (parameters include the magnitude and spatial distribution of charge moments in deep H₂O clouds at 5 bars, and shallow NH₃ clouds at ~1 bar). Results demonstrate that sprites can form in Jupiter's mesosphere when lightning-induced quasi-electrostatic fields exceed the breakdown threshold appropriate for H₂-He mixtures at mesospheric pressures. The simulations reveal the altitude ranges and conditions where electric field-to-neutral density ratios reach critical values for electron avalanche inception and streamer development. Results from simulations of thunderstorms and TLE generation on Saturn will also be presented.