Morphometric studies of the Copernicus and Tycho secondary craters on the moon: Dependence of crater degradation rate on crater size

Basilevsky, A. T.; Козлова, Н. А.; Zavyalov, Igor; Karachevtseva, I. P.; Kreslavsky, M. A.

doi:10.1016/j.pss.2017.06.001

Cited by 24 publications

(10 citation statements)

References 14 publications

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“…On the Moon few secondary craters have been directly measured, but one early study of secondary craters ranging from 200 m to 40 km in diameter found an average depth‐to‐diameter ( H/D) of 0.11 for those with simple morphologies (Pike & Wilhelms, 1978). Measurements for 23 small craters (~250 to 950 m in diameter) identified as secondaries yielded d/D values of ~0.02–0.2 for degraded Copernicus secondaries (with most values clustered around 0.05), and ~0.07–0.14 for somewhat fresher Tycho secondaries (Basilevsky et al, 2018). Additional measurements are available for a few other worlds.…”

Section: Ejecta Fragment Maximum Size‐velocity Distributions (Msvds)mentioning

confidence: 99%

Lunar Secondary Craters and Estimated Ejecta Block Sizes Reveal a Scale‐Dependent Fragmentation Trend

2020

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Planetary impact events eject large volumes of surface material. Crater excavation processes are difficult to study, and in particular the details of individual ejecta fragments are not well understood. A related, enduring issue in planetary mapping is whether a given crater resulted from a primary impact (asteroid or comet) or instead is a secondary crater created by an ejecta fragment. With mapping and statistical analyses of six lunar secondary crater fields (including Orientale, Copernicus, and Kepler) we provide three new constraints on these issues: (1) estimation of the maximum secondary crater size as a function of distance from a primary crater on the Moon, (2) estimation of the size and velocity of ejecta fragments that formed these secondaries, and (3) estimation of the fragment size ejected at escape velocity. Through this analysis, we confirmed and extended a suspected scale‐dependent trend in ejecta size‐velocity distributions. Maximum ejecta fragment sizes fall off much more steeply with increasing ejection velocity for larger primary impacts (compared to smaller primary impacts). Specifically, we characterize the maximum ejecta sizes for a given ejection velocity with a power law and find that the velocity exponent varies between approximately −0.3 and −3 for the range of primary craters investigated here (0.83–660 km in diameter). Data for the Jovian moons Europa and Ganymede confirm similar trends for icy surfaces. This result is not predicted by analytical theories of formation of Grady‐Kipp fragments or spalls during impacts and suggests that further modeling investigations are warranted to explain this scale‐dependent effect.

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Section: Ejecta Fragment Maximum Size‐velocity Distributions (Msvds)mentioning

confidence: 99%

Lunar Secondary Craters and Estimated Ejecta Block Sizes Reveal a Scale‐Dependent Fragmentation Trend

2020

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“…Additionally, at the spatial resolution of the LDRM, our roughness measurements are likely sampling more of the sloping crater walls for the relatively smaller ice‐bearing craters than for the different‐aged craters from the LPI crater database, and crater walls are relatively smoother than other impact crater units (Wang et al, 2019; Zuber et al, 2012). Furthermore, smaller impact craters may degrade and become smoother more quickly than larger craters of the same formation age (Bart & Melosh, 2010a, 2010b; Basilevsky et al, 2018; Mahanti et al, 2018). Due to these multiple variations between the small, ice‐bearing craters and the larger craters analyzed, the roughness values that we find for the interiors of ice‐bearing craters are likely to be lower than the roughness values of similarly aged craters that lack ice.…”

Section: Methods and Resultsmentioning

confidence: 99%

Assessing the Roughness Properties of Circumpolar Lunar Craters: Implications for the Timing of Water‐Ice Delivery to the Moon

Deutsch

Head

Neumann

et al. 2020

Geophysical Research Letters

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The roughness properties of impact craters are valuable indicators of crater degradation and can provide insight into crater ages. We evaluate the roughness of lunar craters from different geologic eras, confirming that young, Copernican craters are distinctly rougher than older craters. We evaluate the potential age of small (less than ~15 km) craters that are thought to host surface ice by quantifying the roughness inside these craters, as well as outside. Interior roughness may be subdued by slope processes or the presence of volatiles. The distribution of ice‐bearing craters is skewed toward roughness values higher than those of pre‐Imbrian craters, although no ice‐bearing craters are within the Copernican‐only domain in roughness space. All of the 15 rough, permanently shadowed craters that are found within the Copernican‐only domain lack water‐ice detections, suggesting that either ice has not been delivered to these young craters or that it has since been destroyed.

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“…However, in high energy impact, the morphologic features of secondary craters and primary craters are similar. Therefore, it is difficult to completely distinguish secondary craters from primary craters based on their morphology, leading to great uncertainty [12,13]. Werner et al [14] estimated that counting all secondary craters would increase the CSFD model age by a factor of two at most.…”

Section: Introductionmentioning

confidence: 99%

Maria Basalts Chronology of the Chang’E-5 Sampling Site

Guo

Liu

2021

Remote Sensing

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Chang’E-5 is the first lunar sample return mission of China. The spacecraft was landed in the northwest of the Procellarum KREEP Terrane (43.0576°N, 308.0839°E) on 1 December 2020 and returned 1731 g samples from a previously unvisited region. The landing area has been proposed as one of the youngest mare basalt units of the Moon and holds important information of lunar thermal evolution and chronology. However, the absolute model ages estimated in previous studies are quite different, ranging from 2.07 Ga to 1.21 Ga. Such significant difference may be caused by (1) different crater counting areas, (2) different crater diameter ranges, (3) effects of secondary craters, and (4) biases in crater identification. Moreover, the accurate landing site was unknown and the ages were estimated over the Eratosthenian-aged mare unit (Em4) instead. In light of the above unsatisfactory conditions, this study seeks to establish a standard crater size-frequency distribution of the CE-5 landing site. We derived the concentrations of FeO and TiO2 to map out the pure basaltic areas where external ejecta deposits are negligible and thus secondary craters are rare. Based on the geochemistry of basaltic ejecta excavated by fresh craters in the mare unit, the FeO concentration threshold for mapping pure basaltic areas is 17.2 wt.%. The morphologically flat subunits in the pure basaltic areas were selected for crater identification and age dating to exclude the contamination of external ejecta to the best as we could. In the Chang’E-5 sampling site subunit, we detected 313 craters with a diameter greater than 100 m and derived the absolute model age as 1.49−0.084+0.084 Ga. The craters identified in all pure basaltic subunits of Em4 gave the model age of 1.41−0.028+0.027 Ga. As least affected by secondary craters, the crater size-frequency distribution of the sample-collected pure basaltic subunit can provide important constraints for lunar cratering chronology function in combination with isotopic age of returned samples.

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Morphometric studies of the Copernicus and Tycho secondary craters on the moon: Dependence of crater degradation rate on crater size

Cited by 24 publications

References 14 publications

Lunar Secondary Craters and Estimated Ejecta Block Sizes Reveal a Scale‐Dependent Fragmentation Trend

Lunar Secondary Craters and Estimated Ejecta Block Sizes Reveal a Scale‐Dependent Fragmentation Trend

Assessing the Roughness Properties of Circumpolar Lunar Craters: Implications for the Timing of Water‐Ice Delivery to the Moon

Maria Basalts Chronology of the Chang’E-5 Sampling Site

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