Cosmic ray exposure ages of features and events at the apollo landing sites

Arvidson, R. E.; Crozaz, G.; Drozd, R. J.; Hohenberg, C. M.; Morgan, Charles G.

doi:10.1007/bf00567518

Cited by 86 publications

(74 citation statements)

References 18 publications

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“…The terrestrial crater record is much too altered, and reliable areas and dates for cratering rate estimates are available only for small numbers of craters. Although we are limited by few absolute age dates on Copernican units [Arvidson et al, 1975], much improved relative ages will be possible with the Clementine multispectral data set. We expect that the use of spectral parameterization of soil maturity [e.g., Charette et al, 1976; Lucey et al, 1995b] could achieve a relative dating accuracy varying from -250 Ma for older Copernican craters decreasing to -20 Ma for craters younger than---100 Ma, because the lunar age-color correlation is strongest for the youngest craters.…”

Section: Discussionmentioning

confidence: 99%

The Phanerozoic impact cratering rate: Evidence from the farside of the Moon

McEwen¹,

Moore²,

Shoemaker³

1997

J. Geophys. Res.

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Abstract. The relatively recent (< 1 b.y.) flux of asteroids and comets forming large craters on the Earth and Moon may be accurately recorded by craters with bright rays on the Moon's farside. Many previously unknown farside rayed craters are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed craters on the lunar nearside are probably significantly older than 1 Ga; rays remain visible over the maria due to compositional contrasts long after soils have reached optical maturity. Most of the farside crust has a more homogeneous composition and only immature rays are visible. The size-frequency distribution of farside rayed craters is similar to that measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed craters matches that of a corrected tabulation of nearside Copernican craters. Hence the presence of bright rays due to immature soils around large craters provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large craters less than -3.2 b.y. old is -3.2 times higher than that of large farside rayed craters alone. This observation can be interpreted in two ways: (1) the average cratering rate has been constant over the past 3.2 b.y. and the base of the Copernican is -1 Ga, or (2) the cratering rate has increased in recent geologic time and the base of the Copernican is less than 1 Ga. We favor the latter interpretation because the rays of Copernicus (800-850 m.y. old) appear to be very close to optical maturity, suggesting that the average Copernican cratering rate was -3 5% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) cratering rate are (1) the densities of small craters superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from welldated terrestrial craters (_< 120 m.y.) and from present-day astronomical observations, and (3) the Proterozoic rate suggested by the crater record of Australia. The hypothesis most consistent with several key observations is that the cratering rate has increased by-2x during the past-300 m.y..

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Section: Discussionmentioning

confidence: 99%

The Phanerozoic impact cratering rate: Evidence from the farside of the Moon

McEwen¹,

Moore²,

Shoemaker³

1997

J. Geophys. Res.

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“…1). The most recent of these are North Ray crater (50 Ma, 1 km in diameter: Arvidson et al, 1975;Maurer et al, 1978;Ulrich, 1981;Lindstrom and Salpas, 1982), South Ray crater (2 Ma, 680 m in diameter: Reed, 1981;Eugster, 1999) and Baby Ray crater (stratigraphically younger than South Ray crater, 130 m in diameter: Reed, 1981). The present day surface morphology of the Apollo 16 landing site and mapped geological unit boundaries are shown in Fig.…”

Section: Post-imbrium Basin Modificationmentioning

confidence: 98%

Re-examination of the formation ages of the Apollo 16 regolith breccias

Joy

Kring

Bogard

et al. 2011

Geochimica et Cosmochimica Acta

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“…The latter possibility seems unlikely as Shoemaker crater is most likely not a young feature in absolute terms (though it is younger than Psyche and Himeros craters), suggested by the number of superposed craters (see "Crater Densities" section). Micrometeorite impact decay of coherent rocks is a slow process (1 mrnIMa; Crozaz et al, 1971;Arvidson et al, 1975) discounting in situ disintegration of boulders. Though direct impact by a macrometeorite will result in catastrophic fragmentation ofboulders, the fact that so many boulders exist on Eros and that superposed craters show Shoemaker crater is ancient, such a process is clearly not efficient on Eros.…”

Section: Block Production By Impact Crateringmentioning

confidence: 99%

The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

155

140

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Abstract-The global high-resolution imaging of asteroid 433 Eros by the Near-Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small S-type asteroid. Eros displays a variety of surface features, and evidence of a substantial regolith. Large scale facets, grooves, and ridges indicate the presence of at least one global planar structure. Directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object. As with other small objects, impact craters dominate the overall shape as well as the small-scale topography of Eros. Depth/diameter ratios of craters on Eros average -0.13, but the freshest craters approach lunar values of -0.2. Ejecta block production from craters is highly variable; the majority oflarge blocks appear to have originated from one 7.6 km crater (Shoemaker). The interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of Phobos. This lack of mechanical boundaries, and the abundant evidence of regolith in nearly every high-resolution image, suggests a gradation in the porosity and fracturing with depth. The density of small craters is deficient at sizes below -200 m relative to predicted slopes of empirical saturation. This characteristic, which is also found on parts ofPhobos and lunar highland areas, probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith. Eros displays a variety ofregolith features, such as debris aprons, fine-grained "ponded" deposits, talus cones, and bright and dark streamers on steep slopes indicative ofefficient downslope movement ofregolith. These processes serve to mix materials in the upper loose fragmental portion ofthe asteroid (regolith). In the instance of "ponded" materials and crater wall deposits, there is evidence of processes that segregate finer materials into discrete deposits. The NEAR observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic. Future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the NEAR Shoemaker spacecraft.

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Cosmic ray exposure ages of features and events at the apollo landing sites

Cited by 86 publications

References 18 publications

The Phanerozoic impact cratering rate: Evidence from the farside of the Moon

The Phanerozoic impact cratering rate: Evidence from the farside of the Moon

Re-examination of the formation ages of the Apollo 16 regolith breccias

The geology of 433 Eros

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