Pluto’s high obliquity and eccentric orbit lead to significant changes in solar insolation over latitudes and seasons. Its microbar-pressure, nitrogen-dominated atmosphere is supported by vapor-pressure equilibrium with the surface ices. The properties and existence of the atmosphere thus depend critically on surface conditions. Models of volatile transport have been employed to anticipate Pluto’s atmospheric evolution. Some models predict atmospheric contraction/collapse over the coming decades, while others show the atmosphere persisting throughout Pluto’s entire orbital period. Pluto’s atmosphere is of interest in terms of better understanding atmospheres (or the lack thereof) on large trans-Neptunian objects as well as the long-term evolution of icy bodies with variations in solar insolation.
We have an ongoing program to predict and observe stellar occultations by Pluto, which has identified a pressure increase between 1988 and 2002, revealed waves in the upper atmosphere, detected haze in the lower atmosphere, and characterized atmospheric changes over decadal timescales. NASA’s New Horizons spacecraft provided a wealth of data on Pluto’s atmosphere during the 2015 flyby that can be placed into context through continued observations of ground-based stellar occultations. Here, we report on the results from the past four years of Pluto occultation observations, including measurements of atmospheric size and pressure. Additional observations are scheduled for the remainder of 2021.
This work is funded by NASA grant 80NSSC21K0432.