Thickness determinations of the lunar surface layer from lunar impact craters

Abstract

Small, fresh lunar craters with normal, central‐mound, flat‐bottomed, and concentric geometry are widespread on maria surfaces. The same types of craters have been produced in the laboratory by impacting projectiles against targets consisting of loose, granular, noncohesive materials overlying cohesive substrates. The mechanics of formation of each laboratory crater type is described, and evidence is offered that the corresponding types of lunar craters are of impact origin. Extensive studies of the effects of lunar impact variables on the conditions of formation of these crater types show that a previously described statistical method can be used to determine the thickness of the lunar surfaces layer within narrow limits. Two independent methods for determining the layer thickness at specific points are presented. Thickness estimates of the Surveyor 1 site obtained previously from study of medium‐resolution Orbiter 1 photographs are re‐evaluated by using subsequently obtained high‐resolution photographs, and thickness determinations of two additional areas are presented. The different areas examined have different surface layer thickness. The fragments of the surface are certainly partly of impact origin, but volcanic contributions may also be present. The maria substrates are probably composed of volcanic flow rocks with interbeds of fragmental material.

The origin of Vesta’s crust: Insights from spectroscopy of the Vestoids

“…This depth of regolith, which is several orders of magnitude greater than that predicted for the lunar regolith (e.g. Quaide and Oberbeck, 1968;Cooper et al, 1974;Wilcox et al, 2005), seems unlikely. 2.…”

The geology of 433 Eros

“…7). On the Moon, interior terracing of 100 m scale mare craters has been proposed to indicate excavation through a loose unconsolidated regolith to a coherent substrate Quaide, 1967, 1968;Quaide and Oberbeck, 1968). This morphology is rarer in lunar highland craters, indicating a thicker or more gradational regolith or a lack of a coherent substrate.…”

“…No analogous ponded deposits have been identified on Phobos in published work (Thomas et a!., 2000) and our examination of Mars orbiter camera (MOC) images ofPhobos have revealed no planar or flat floored craters similar to ponds found on Eros. Lunar crater morphologies were cataloged from high-resolution Lunar Orbiter images (1 m/pixel and better) in a series ofpapers (see discussion above; Quaide, 1967, 1968;Quaide and Oberbeck, 1968). These studies reported four distinct morphologies (Q&O craters) for small mare craters, related to an interface between a regolith and a coherent substrate-none of these morphologies is similar to the ponded deposits found on Eros (Figs.…”

Dynamic tensile strength of lunar rock types

“…Excavation processes and consequently the final ejecta distribution and partitioning of energy strongly depend upon the brittle tensile failure characteristics of the rock, probably more so than compressional failure mechanisms. Laboratory experiments and numerical modeling show that crater evolution and ultimate shape are sensitive to the failure behavior of rocks [Quaide and Oberbeck, 1968; O'Keefe and •4hrens, 1976; Melosh, 1977].…”