Possible Transient Luminous Events Observed in Jupiter's Upper Atmosphere

Eleven transient bright flashes were detected in Jupiter's atmosphere using the ultraviolet spectrograph instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ∼1.4 ms. The spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 260 km above the 1‐bar level. Based on these characteristics, we suggest that these are observations of transient luminous events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that occur in the Earth's upper atmosphere in response to tropospheric lightning strikes. This is supported by visible light imaging, which shows cloud features typical of lightning source regions at the locations of several of the bright flashes. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on Jupiter. Plain Language Summary The Juno spacecraft has been in orbit around Jupiter since 2016. One of the instruments on this spacecraft is an ultraviolet spectrograph (UVS), which is primarily used to make ultraviolet images of Jupiter's auroras. During the first 4 years of the mission, the UVS has observed 11 transient bright flashes. These bright flashes look similar to lightning, but are located much higher in the atmosphere than the cloudy regions of Jupiter where lightning is generated. We suggest that these are observations of transient luminous events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that produce spectacular flashes of light very high in the Earth's atmosphere in response to lightning strikes between clouds or between clouds and the ground. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on other planets, including Jupiter. Comparing and contrasting TLE observations between Jupiter and Earth will improve our understanding of electrical activity in planetary atmospheres. Key Points Eleven transient bright flashes were observed by the ultraviolet instrument on the Juno mission The flashes have an average duration of 1.4 ms, are located 260 km above the 1‐bar level and are dominated by H2 emission The