Evidence for a rapid decrease in Pluto's atmospheric pressure revealed by a stellar occultation in 2019

TL;DR

This study reports a potential rapid decrease in Pluto's atmospheric pressure based on a 2019 stellar occultation, challenging previous trends of increasing pressure and suggesting possible seasonal or orbital effects.

Contribution

First observational evidence of a significant and rapid decline in Pluto's atmospheric pressure since 2012, highlighting the need for further confirmation and theoretical modeling.

Findings

Indicates a possible 21% pressure drop between 2016 and 2019.

Suggests the decrease may be due to nitrogen condensation in Sputnik Planitia.

Contradicts previous reports of monotonic pressure increase.

Abstract

We report observations of a stellar occultation by Pluto on 2019 July 17. A single-chord high-speed (time resolution $= 2\,$s) photometry dataset was obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope (Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an existing Pluto's atmospheric model. We find the lowest pressure value at a reference radius of $r = 1215~{\rm km}$ among those reported after 2012, indicating a possible rapid (approximately $21^{+4}_{-5} \%$ of the previous value) pressure drop between 2016 (the latest reported estimate) and 2019. However, this drop is detected at a $2.4\sigma$ level only and still requires confirmation from future observations. If real, this trend is opposite to the monotonic increase of Pluto's atmospheric pressure reported by previous studies. The observed decrease trend is possibly caused by ongoing ${\rm N_2}$ condensation processes in the Sputnik Planitia glacier associated with an orbitally driven decline of solar insolation, as predicted by previous theoretical models. However, the observed amplitude of the pressure decrease is larger than the model predictions.