Fresh impact ejecta deposits on the lunar surface can be characterized as heterogeneous mixtures of boulders, cobbles, and fine-grained regolith that are deposited on the lunar surface during the impact crater formation process. Over time, the boulders associated with ejecta deposits break down into fine-grained regolith due to a combination of bombardment and thermal fatigue. Several qualitative observations of old (>2.0 Ga) kilometer-scale lunar impact ejecta deposits made here in high-resolution images reveal tens of large (>1 m) boulders associated with kilometer-scale crater rims and near-proximal ejecta deposits on the lunar maria. These observations went undescribed in prior measurements of lunar boulder breakdown which suggested that lunar boulders should be destroyed in <300 Myr due to micrometeoroid impacts and other processes (e.g., Basilevsky et al., 2015). Here, we use a combination of radar and thermal-infrared data from the Lunar Reconnaissance Orbiter spacecraft to show that kilometer-scale impact crater rims exhibit elevated rock abundances for the lifetime of the lunar maria. We interpret these results as indicating that boulders are continually being uncovered at crater rims due to downslope movement of the overlying regolith. Moreover, rocks found at crater rims that have been exhumed from depth in geologically recent times are locally derived and unlikely to have come from other areas of the Moon. Future collection of lunar samples at crater rims will serve to mitigate the potential for sample contamination from distal sources, helping to ensure accurate geologic interpretations from the collected samples.

The variety of tectonic features on the Moon indicates that the lunar lithosphere has undergone a complex deformational history. Lobate scarps and wrinkle ridges are two such tectonic features that have resulted from compressional stresses. The crisp morphologies and cross cutting relations associated with a global population of lobate scarps have been cited as evidence for their recent (<50 Ma) formation, but observations of recently active wrinkle ridges have yet to be made on a similar scale. Here, we present new observations of 1,127 recently active wrinkle ridge segments on the lunar nearside mare. Our results indicate that recently active wrinkle ridges are distributed across ~90% of nearside mare basins – occurring in clusters of ~10–100 ridge segments with a mean segment length of 4.4 km. The magnitudes and orientations of these recently active wrinkle ridges are consistent with the hypothesis of formation by orbital recession stresses.