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.
In 2002, the PAL was involved in another prediction and analysis of a stellar occultation by Pluto (P131.1). Data were obtained on a number of different telescopes for the P131.1 occultation, and the light curves were analyzed with atomospheric models as well as inversion. The most startling outcome of these observations was a rather dramatic change in Pluto's atomosphere since the previous observation, in 1988. While carrying out extensive astrometry for the prediction of this occultation, a significant wobble was discovered in Pluto's found position from its ephemeris. The exact cause of the residuals remains unknown.
Current research includes photometric and astrometric analyses of Pluto, as well as continuing characterization of Pluto's atmosphere.