Meridional Variations of C2H2 in Jupiter's Stratosphere From Juno UVS Observations

The Ultraviolet Spectrograph (UVS) instrument on the Juno mission records far‐ultraviolet reflected sunlight from Jupiter. These spectra are sensitive to the abundances of chemical species in the upper atmosphere and to the distribution of the stratospheric haze layer. We combine observations from the first 30 perijoves of the mission in order to study the meridional distribution of acetylene (C2H2) in Jupiter's stratosphere. We find that the abundance of C2H2 decreases toward the poles by a factor of 2–4, in agreement with previous analyses of mid‐infrared spectra. This result is expected from insolation rates: near the equator, the UV solar flux is higher, allowing more C2H2 to be generated from the UV photolysis of CH4. The decrease in abundance toward the poles suggests that horizontal mixing rates are not rapid enough to homogenize the latitudinal distribution. Plain Language Summary The Ultraviolet Spectrograph instrument on the Juno mission to Jupiter is primarily used to study the planet's ultraviolet auroras, but also records reflected sunlight from the planet's upper atmosphere. These ultraviolet reflected sunlight observations can be used to measure the abundances of different gases in Jupiter's stratosphere. In this study, we focus on one prominent molecule, acetylene, and study how its abundance varies with latitude. We find that its abundance decreases toward Jupiter's poles, which agrees with previous results obtained from studying the same molecule with infrared observations. Key Points Ultraviolet reflected sunlight observations from Juno Ultraviolet Spectrograph were used to study the C2H2 abundance in Jupiter's stratosphere The stratospheric C2H2 abundance decreases at high latitudes, in agreement with previous studies using infrared data The latitudinal distribution of C2H2 can be used to constrain horizontal mixing rates