Pluto and Charon
In 1998,the PAL was involved in the prediction and observation of a stellar occultation by Pluto using NASA's Kuiper Airborne Observatory. The resulting data conclusively demonstrated that Pluto has an atmosphere, the upper part of which was found to be essentially clear. Since then, the group has been actively involved in atmospheric analysis of Pluto, including modeling the lower part of the atmosphere as either an extinction layer or sharp thermal gradient and refining the inversion technique as applied to stellar occultation data.
Short of sending a spacecraft, stellar occultations are the most sensitive method to study Pluto's atmosphere. Observations that we took in 2002 showed that the microbar-level atmosphere roughly doubled in size since 1988. We have taken occultation data between 2006 and the present to continue studying the atmospheric pressure and size. Further, our data from 2007 revealed waves in the upper atmosphere and in 2011 and 2015 (among other years) suggested that there was haze in the lower atmosphere. We used a 2005 occultation observation by Pluto's largest moon, Charon, to place tight constraints on its size and any atmosphere.
Pluto's atmosphere is in vapor-pressure equilibrium with its surface. Therefore, the properties of the atmosphere are tightly tied to the properties of the surface ice. Pluto has a high obliquity and high orbital eccentricity, which lead to varying amounts of solar flux on the surface. The atmosphere changes with time, accordingly, and measurements of the atmosphere can be used to better understand the characteristics of the ice. Current research includes continuing observations of stellar occultations by Pluto in order to study its evolving atmosphere.
Please see our Pluto and Charon publications.