Changes in Pluto’s Atmosphere Based on Stellar Occultation Data from 2017 to 2023

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Abstract Pluto’s tenuous atmosphere has microbar-level pressure and is composed primarily of N 2 , with a variable haze. Its eccentric orbit, combined with high obliquity, leads to significant changes in solar insolation throughout the Plutonian year. The atmosphere is supported by vapor pressure equilibrium with the surface ices; thus, surface changes are coupled with the atmospheric properties. Volatile-transport models have anticipated Pluto’s atmospheric evolution: predictions range from collapse over the coming decades to an atmosphere that remains. Previous work claims that Pluto’s atmospheric pressure monotonically increased from 1988 through 2016, that the atmosphere began freezing out in 2018–2019, and that there was a plateau as of 2020. Here we report results from 10 stellar occultations by Pluto between 2017 August and 2023 July. Four events were multichord, while six were from single sites. Our results indicate a pressure plateau between the New Horizons flyby in 2015 through roughly 2021 and suggest that the atmospheric pressure has started to drop. Comparing data taken 2015–2021 and 2022, the clear-atmosphere pressure at 1275 km decreased 7% ± 6%, and it dropped 16% ± 2% for pressure at 1215 km when including haze. From 2017 to 2023, the upper atmospheric structure is consistent, while there is a change in light-curve slope in the lower atmosphere. This change of slope is consistent with haze particles settling over yearly or shorter timescales. Spikes in one light curve are indicative of intermittent buoyancy waves. More data are needed to confirm a recent pressure change.

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