Discovery of a Dust Sorting Process on Boulders Near the Reiner Gamma Swirl on the Moon

In a database of lunar fractured boulders (Rusch & Bickel, 2023, ), we found boulders with reflectance features dissimilar to previously known morphologies. We performed a photo-geologic investigation and determined that the features correspond to a dust mantling on top of boulders with a unique photometric behavior. We next performed a photometric model inversion on the dust mantling using Bayesian inference sampling. Modeling indicates that the dust photometric anomaly is most likely due to a reduced opposition effect, whereas the single scattering albedo is not significantly different from that of the nearby background regolith. This implies a different structure of the dust mantling relative to the normal regolith. We identified and discussed several potential processes to explain the development of such soil. None of these mechanisms can entirely explain the multitude of observational constraints unless evoking anomalous boulder properties. Further study of these boulders can shed light on the workings of a natural dust sorting process potentially involving dust dynamics, a magnetic field, and electrostatic dust transport. The presence of these boulders appears to be limited to the Reiner K crater near the Reiner Gamma magnetic and photometric anomaly. This close spatial relationship further highlights that poorly understood processes occur in this specific region of the Moon. The study of rocks on the surface of the Moon is important to understand the processes forming and modifying the lunar crust as well as the processes modifying rocks after their formation. The lunar rocks resting on the surface can be studied by imaging them with an orbital camera and analyzing their shape and reflectance. Here we report on the finding of a new type of brightness feature on rocks. This finding was made possible by scrutinizing a catalog of split lunar rocks. The brightness feature is found to be unique because of its rare occurrence, localization limited to near the Rainer Gamma magnetic anomaly, and association with some but not all rocks of the crater Reiner K. The feature is a dust deposit with a potentially uncommon physical structure. In a catalog of lunar boulder images, we find a new type of reflectance feature associated with bouldersThe feature is likely a dust mantling with unique photometric propertiesSeveral formation scenarios are discussed