Quantifying crater production and regolith overturn on the Moon with temporal imaging

Abstract

Random bombardment by comets, asteroids and associated fragments form and alter the lunar regolith and other rocky surfaces. The accumulation of impact craters over time is of fundamental use in evaluating the relative ages of geologic units. Crater counts and radiometric ages from returned samples provide constraints with which to derive absolute model ages for unsampled units on the Moon and other Solar System objects. However, although studies of existing craters and returned samples offer insight into the process of crater formation and the past cratering rate, questions still remain about the present rate of crater production, the effect of early-stage jetting during impacts and the influence that distal ejecta have on the regolith. Here we use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) temporal ('before and after') image pairs to quantify the contemporary rate of crater production on the Moon, to reveal previously unknown details of impact-induced jetting, and to identify a secondary impact process that is rapidly churning the regolith. From this temporal dataset, we detected 222 new impact craters and found 33 per cent more craters (with diameters of at least ten metres) than predicted by the standard Neukum production and chronology functions for the Moon. We identified broad reflectance zones associated with the new craters that we interpret as evidence of a surface-bound jetting process. We also observe a secondary cratering process that we estimate churns the top two centimetres of regolith on a timescale of 81,000 years-more than a hundred times faster than previous models estimated from meteoritic impacts (ten million years).

Impact Gardening as a Constraint on the Age, Source, and Evolution of Ice on Mercury and the Moon

“…The power index of the reworking depth ( ) must be negative and must be for the model to describe physical reality—small, shallowly overturning impacts are more likely than large, deeply overturning impacts. Fortunately, most predictions of CPFs for secondary craters, which dominate the mechanical churning of the uppermost meter or so, have relatively steep power indices ( ; e.g., Bierhaus et al, ; McEwen et al, ; Speyerer et al, ), satisfying the requirement that be .…”

Dust-aggregate impact into granular matter: A systematic study of the influence of projectile velocity and size on crater formation and grain ejection

“…Such impacts are of considerable relevance in an astrophysical context. The surfaces of regolith-covered moons and asteroids are constantly subjected to impacts by dust particles and micro-meteorites, with consequences on the composition and mechanical properties of these surfaces (Schwartz et al 2014;Speyerer et al 2016).…”

An Examination of Several Discrete Lunar Nearside Photometric Anomalies Observed in Lyman‐α Maps

“…However, most new features created by impact, and this young, have also shown thermophysical properties consistent with lunar cold spots (Bandfield et al, ; Hayne et al, ). Perhaps, an argument against a younger age of origin (or at least a contemporary origin) is that none of these anomalies exhibit characteristics of cold spots recently discovered and predominantly associated with young, small craters and their ejecta (at least in part, the area of cold spots have been suggested to present a volume of material more than could realistically fit back into the associated crater; Hayne et al, ; Speyerer et al, ).…”