Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.