Evidence for Possible Clouds in Pluto's Present-day Atmosphere

Several trace constituents can reach saturation vapor pressure in Pluto's present-day atmosphere (PDA). As such, we describe a search for discrete cloud features in Pluto's atmosphere using New Horizons data obtained on 2015 July 14-15, during the Pluto flyby closest approach. We report that the PDA is at least largely (>99% by surface area) free of discrete clouds. We also report a handful of features that may plausibly be clouds, all of which were detected obliquely and at high-phase-angle observing geometry. No cloud candidates were identified away from the terminators or in low-phase (backscattering geometry) images.