PIT CRATER CHAINS AND SUBTERRANEAN TECTONIC CAVES

Subterranean void spaces on planetary bodies are a critical area of study for both astrobiology and in situ resource utilization (ISRU). Common cave forming mechanisms such as lava tubes are being studied as subsurface areas of interest and have been interpreted on the moon and Mars. However, lava tubes are relatively rare in the solar system, and where found, often limited in spatial extent (e.g., lava tubes are typically confined to a single lava flow). Alternatively, the ubiquitous nature of extensional fractures, normal faulting, and pit crater chain formations found on terrestrial planets, asteroids and icy moons suggests that dilational faulting may be the dominant formation mechanism for creating subsurface void space.

Dilational faulting can occur when extensional strain is applied across mechanically stratified layers, or where hybrid mode failure (Mode I opening combined with either Mode II sliding and/or Mode III tearing) occurs under low differential stress. Mechanical stratigraphy influences where faults nucleate, the type of failure mode, the strike/dip geometry, and the degree and distribution of displacement along the fault. In particular, the stratigraphic layering of mechanically strong rock (e.g., basalt flow) with relatively weak rock (e.g., non-lithified pyroclastic deposits, unconsolidated regolith) often found on planetary bodies lends itself to the formation of dilational faults. The geometry of these dilational faults in the subsurface have a significant influence on the flow and storage of fluids and volatiles as well as mineral deposition on Earth, and likely plays a similar role on solid bodies in our solar system. Whether the target is groundwater/ice, methane, metals, minerals or other vital ISRU, dilational fault systems play a major role in controlling where these resources may be found. Fortunately, dilational faults often reveal themselves in the form of collapsed pit crater chains, which can usually be identified in visual imagery and topographic datasets. Quantifying pit crater chains and their underlying fault zones can, in turn, help constrain the degree of potential void space available in the subsurface as well as help define the permeability architecture.