The nature of crater rays: The Copernicus example

Pieters, C. M.; Adams, John B.; Mouginis-Mark, P. J.; Zisk, S. H.; Smith, Matthew D.; Head, J. W.; McCord, T. B.

doi:10.1029/jb090ib14p12393

Cited by 93 publications

(70 citation statements)

References 35 publications

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“…The formulation reduces by half the difference from 5.00 of the calculated µ value (from Oberbeck's equation). Mixing ratio values less than 5.00 are maintained as that value is the highest µ value validated by remote observations (Pieters et al 1985;Head et al 1993;Blewett et al 1995). Reducing mixing ratio values also act to reduce the effectiveness of the secondary cratering process to be more consistent with experimental impacts by Schultz and Gault (1985).…”

Section: Discussionmentioning

confidence: 99%

The lunar‐wide effects of basin ejecta distribution on the early megaregolith

Petro

Pieters

2008

Meteorit & Planetary Scien

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Abstract-The lunar surface is marked by at least 43 large and ancient impact basins, each of which ejected a large amount of material that modified the areas surrounding each basin. We present an analysis of the effects of basin formation on the entire lunar surface using a previously defined basin ejecta model. Our modeling includes several simplifying assumptions in order to quantify two aspects of basin formation across the entire lunar surface: 1) the cumulative amount of material distributed across the surface, and 2) the depth to which that basin material created a well-mixed megaregolith. We find that the asymmetric distribution of large basins across the Moon creates a considerable nearside-farside dichotomy in both the cumulative amount of basin ejecta and the depth of the megaregolith. Basins significantly modified a large portion of the nearside while the farside experienced relatively small degrees of basin modification following the formation of the large South Pole-Aitken basin. The regions of the Moon with differing degrees of modification by basins correspond to regions thought to contain geochemical signatures remnant of early lunar crustal processes, indicating that the degree of basin modification of the surface directly influenced the distribution of the geochemical terranes observed today. Additionally, the modification of the lunar surface by basins suggests that the provenance of lunar highland samples currently in research collections is not representative of the entire lunar crust. Identifying locations on the lunar surface with unique modification histories will aid in selecting locations for future sample collection.

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Section: Discussionmentioning

confidence: 99%

The lunar‐wide effects of basin ejecta distribution on the early megaregolith

Petro

Pieters

2008

Meteorit & Planetary Scien

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“…This topic is further discussed below. We note that the modeled %PriFrags in the deposits at 150 km from the center of Copernicus is ~11%, compared with ~20-25% obtained by Pieters et al (1985) on the basis of spectral data.…”

Section: Crater Counts; Copernicus Secondary Cratersmentioning

confidence: 97%

On estimating contributions of basin ejecta to regolith deposits at lunar sites

Haskin¹,

Moss²,

McKinnon³

2003

Meteorit & Planetary Scien

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On estimating contributions of basin ejecta to regolith deposits at lunar sites Oberbeck 1975), and takes into account the size distribution of the individual fragments ejected from the primary crater. Using the model, we can estimate, for an area centered at the chosen location of interest, the average distribution of thicknesses of basin ejecta deposits within the area and the fraction of primary ejecta contained within the deposits. Model estimates of ejecta deposit thicknesses are calibrated using those of the Orientale Basin (Moore, Hodges, and Scott 1974) and of the Ries Basin (Hörz, Ostertag, and Rainey 1983). Observed densities of secondary craters surrounding the Imbrium and Orientale Basins are much lower than the modeled densities. Similarly, crater counts for part of the northern half of the Copernicus secondary cratering field are much lower than the model predicts, and variation in crater densities with distance from Copernicus is less than expected. These results suggest that mutual obliteration erases essentially all secondary craters associated with the debris surge that arises from the impacting primary fragments during ballistic sedimentation; if so, a process other than ballistic sedimentation is needed to produce observable secondary craters. Regardless, our ejecta deposit model can be useful for suggesting provenances of sampled lunar materials, providing information complementary to photogeological and remote sensing interpretations, and as a tool for planning rover traverses (e.g., Haskin et al. 1995Haskin et al. , 2002.

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“…We use the inferred ages of Tycho, Copernicus, Aristillus, and Autolycus to cross-check consistency and to provide calibration. Many craters have jetting and clumping of their ejecta and therefore are not radially symmetric [Shoemaker, 1966;Pieters et al, 1985]. Figures 3a and 3b show traces through the raw OMAT data images for six example craters to illustrate the range of irregularities typically encountered in the maturity of the rayed ejecta.…”

Section: Relative Ages Of Craters From Omat Profiles Wementioning

confidence: 99%

Optical maturity of ejecta from large rayed lunar craters

Grier¹,

McEwen²,

Lucey³

et al. 2001

J. Geophys. Res.

118

111

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Abstract. Lucey et al. [2000] have developed a methodology for extracting an optical maturity parameter (OMAT) from multispectral Clementine images. The OMAT parameter characterizes the overall maturity of lunar soils and crater ejecta by changes in reflectance spectra. Using these OMAT images, we surveyed large craters (->20 km diameter) on the Moon that had previously been mapped as possessing or possibly possessing rayed ejecta. We generated average radial profiles of OMAT values for rays of these large craters. From these profiles we classified the craters into three relative age groups: (1) older than Copernicus (inferred age of --•810 Myr), (2) intermediate, and (3) as young or younger than Tycho (inferred age of --•109 Myr). We suspect that there is a bias to our classification scheme, such that the OMAT profiles of smaller craters look like that of larger but older craters. Nevertheless, some large craters, such as Eudoxus (67 km) and Aristillus (55 km), are now known from this study to have optically mature ejecta and therefore are suspected to be older than Copernicus (this is consistent with an age of 1.

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The nature of crater rays: The Copernicus example

Cited by 93 publications

References 35 publications

The lunar‐wide effects of basin ejecta distribution on the early megaregolith

The lunar‐wide effects of basin ejecta distribution on the early megaregolith

On estimating contributions of basin ejecta to regolith deposits at lunar sites

Optical maturity of ejecta from large rayed lunar craters

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