Geologic Investigation of Deep Simple Craters in the Lunar Simple‐to‐Complex Transition

Abstract

From a group of well‐preserved lunar simple craters in the 15‐ to 20‐km diameter range and with the help of Lunar Orbiter Laser Altimeter topography data, we identified a subset of eight deep craters (depth/diameter ratio > 0.20). These craters are in the regions around the mare‐highlands boundaries, which are characterized as having the highest porosity on the lunar surface. To understand the cratering mechanics behind the formation of these craters, a geologic investigation of the terrains of these craters was performed. We evaluated the depth/diameter ratios of smaller simple craters surrounding several 15‐ to 20‐km diameter craters, analyzed the morphometry of the craters, and visually examined the cavities using multiple data sets. We conclude that deep transient cavities were formed from compaction of porous target material. The result was a deeper than normal simple crater without an identifiable increase in the volume of excavated material, as inferred from the craters' rim heights and shapes. While all of these craters formed in areas of high porosity, not all craters in high‐porosity regions are deep. It may be that some unusual impactor property is also required to produce a deep crater, such as a high velocity impact, a near‐vertical impact, or a dense impactor that yielded a large penetration depth.

Impact Crater Morphometry on Pluto: Implications for Surface Composition and Evolution

“…One of our more perplexing findings is the existence of especially deep craters (R < 0) in the southeast region of Cthulhu Macula (Figures 5 and 6; Robbins et al 2021). Impact velocity can affect the depth of a "pristine" crater (Silber et al 2017), but the fact that there is a cluster of deep craters suggests that it is a regional effect in Cthulhu Macula (e.g., due to material properties; Chandnani et al 2019). Robbins et al (2021) noted the presence of these anomalously deep craters and excluded them when developing their depth-to-diameter fits.…”

“…Robbins et al (2021) noted the presence of these anomalously deep craters and excluded them when developing their depth-to-diameter fits. They noted that these are indicative of unique target properties (e.g., increased porosity; Chandnani et al 2019;Robbins et al 2021). Most of the deep craters are outside the primary dark region of Cthulhu Macula, which may suggest that the effect is related to cryovolcanism in the neighboring Wright group, where the fresher ice may have different properties from the rest of the crust (Singer et al 2022).…”

“…Our analysis includes the examination of regional variations in crater modification by analyzing crater relative depths (R = 1 − d pristine /d current ) as a metric of crater modification (Forsberg-Taylor et al 2004). These depths are also a reflection of bedrock properties, since target strength influences crater morphometry (e.g., Schenk 2002;Stern et al 2015a;Chandnani et al 2019;Umurhan et al 2021; see Section 1.2).…”

Influence of Target Properties on Wall Slumping in Lunar Impact Craters Within the Simple‐To‐Complex Transition

“…Target heterogeneities such as interlayering of different lithologies or unconsolidated sediments with cohesive substrate can create strength variations in the target and trigger cavity collapse, thereby forming slump features and/or terraces and/or central peaks. This may be why a smaller diameter has been observed for the onset of transitional and complex craters in layered targets (Chandnani et al, 2019a(Chandnani et al, , 2019bCintala et al, 1977;Cooper, 1977;Dence, 1972;Osinski et al, 2018;Pike, 1980a;Quaide & Oberbeck, 1968;Roddy, 1977;Senft & Stewart, 2008;Smith & Hartnell, 1978;Stewart & Valiant, 2006). Impact on a target characterized by spatial variations in strength can also lead to cavity collapse features.…”

“…In previous work, Chandnani et al. (2019a, 2019b) examined the global set of well‐preserved craters between 15 and 20 km in diameter, a subset of the transition zone, to identify the causes for morphology differences. As part of that effort, Chandnani et al.…”