Transient Luminous Events observed in Jupiter's upper atmosphere

Abstract:

The Ultraviolet Spectrograph (UVS) is a long-slit imaging spectrograph on the Juno mission, which has been in orbit around Jupiter since July 2016. UVS covers the 68-210 nm wavelength range with a spectral resolution of 1.3-3.0 nm, and makes use of the spacecraft's rotation to build up an ultraviolet image as the instrument slit sweeps across the planet. The primary purpose of UVS is to map Jupiter's far-UV auroral emissions, but the instrument has also detected seven transient bright flashes, which we suggest may be Transient Luminous Events in Jupiter's upper atmosphere. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ~1.6 ms. Their 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. As seen by UVS, the emissions are point sources, with maximum widths of 600-1800 km. These properties are consistent with the predicted properties of Sprites or Elves in Jupiter’s atmosphere (Yair et al., 2009, doi: 10.1029/2008JE003311, Luque et al., 2014, doi: 10.1002/2014JA020457). While tropospheric lightning has been frequently observed in Jupiter’s atmosphere, including by several other instruments on the Juno mission, Transient Luminous Events have not previously been observed in a planet other than Earth.