New Horizons Observations of an Ultraviolet Stellar Occultation and Appulse by Pluto's Atmosphere

A few hours after its encounter with Pluto, the Alice UV instrument on the New Horizons spacecraft observed the simultaneous stellar occultation and appulse of two UV-bright stars, HD 43153 and HD 42545, respectively. As during the solar occultation that occurred immediately prior, the transmission of starlight through Pluto's atmosphere was sensitive to absorption by N2, CH4, C2H6, C2H2, C2H4, and haze. The line of sight to each star passed over different areas of Pluto from those probed by the solar occultation, providing insight into the degree of spatial and diurnal variability of atmospheric composition on Pluto. In this work, we report the profile of CH4 derived from both the stellar occultation and appulse observation, as well as the profiles of C2H6, C2H2, C2H4, and haze for the stellar occultation only. We compare these profiles to the solar occultation results and discuss implications for atmospheric variability on Pluto.