Juno/UVS Observations of Transient Luminous Events in Jupiter's Upper Atmosphere

The Ultraviolet Spectrograph (UVS) on the Juno spacecraft has observed 11 bright flashes in Jupiter's upper atmosphere over the course of the first four years of the mission. 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 far-ultraviolet spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 250 km above the 1-bar level. The emissions are consistent with point sources, which corresponds to maximum widths of 500-2000 km. 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 or sprites, two types of TLEs that occur in Earth's upper atmosphere in response to tropospheric lightning strikes. Visible light imaging 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.