Clusters of irregular patches on the Moon: A new GIS-based catalog

Abstract

The aim of this work was to systematically map cluster-forming Irregular Patches (IPs) on the Moon. These features, formerly termed “Irregular Mare Patches”, are enigmatic features situated on the near side of the Moon, mostly in mare regions. IPs are pristine-looking features with textures at the meter scale, suggesting they formed millions of years ago on top of several-billion-year-old mare basalts. Morphologic and spectral studies could not provide conclusive evidence of their formative processes, or their age. Theories on their formation concentrate around three conflicting models - that they are formed by compact basalts and are only a few tens of millions of years old; that they are formed by mass wasting processes capable to remove regolith to this day; or that they are composed of lava foams and their age is the same as the host terrain's, i.e. billions of years. We present a GIS-based analysis to examine which formation model is supported by their geography. Previous catalogs mapped IPs ambiguously, with one single coordinate representing one unit or a group of units, with many isolated units around them remaining unmapped. To change that, we mapped isolated IPs individually as polygons because we wanted to reveal their areas and their local-scale distribution patterns, which were not identifiable from previous mapping efforts. We named the isolated, elemental depressions Irregular Patches to differentiate them from previous works. After the mapping, we grouped these IPs into clusters. This new mapping revealed that over 2700 Irregular Patches form more than 100 clusters, often displaying characteristic patterns. Their geologic context suggests that these patterns are controlled by subsurface geologic structures and processes. This way even without penetrating radar, recognizing the clustered nature of IPs on the Moon enables us to infer details of the IP hosting regions' subsurface structures and infer subsurface processes that led to their formation.