Recent boulder falls on the Moon

Lunar boulder fall tracks indicate recent surface activity, however, to date there has been no systematic attempt to identify recent fall locations and it remains elusive that how recent the falls actually are. Our study mapped the recent boulder falls located within ±40° latitude, identified by the presence of boulder bounce-induced ejecta along the tracks referred to as Boulder Fall Ejecta (BFE). Our comprehensive survey revealed 245 tracks with ∼373 km total length, which are clearly distinguishable from classical boulder tracks, which lack such ejecta. We found 46 % of BFE tracks are located on the Mare and 54 % in Highland regions, suggesting relatively more falls in the Mare region, as there are fewer steep slopes here. We report that ∼62 % of our mapped locations host multiple BFE tracks, which indicates more boulder falls within those regions. Placing the BFE tracks with their contextual region revealed the first geomorphic evidence for impact ejected/triggered boulder falls. We find that fresh craters hosting the BFE tracks are a few 100 Ka old, meaning that the BFE tracks are even more recent. We observed BFE tracks adjacent to the Lee-Lincoln scarp at the Apollo17 site and a few other locations neighboring to Apollo seismic epicenters/wrinkle ridge/lobate scarps, which we hypothesize as potential hotspots. We infer from the spatial distribution of these BFE tracks that various triggers have played a role in causing the recent falls. With these newly found BFE tracks, the Moon joins Earth and Mars, with records of recent boulder falls driven by multiple sources suggesting a sporadically active Moon. Such regions could be potential landing sites for future missions to understand the recent surface/subsurface activity on the Moon.