A lunar soil evolution model

Mendell, W. W.; McKay, D. S.

doi:10.1007/bf00567520

Cited by 18 publications

(11 citation statements)

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“…The excavation ratio of 1.07 implies that the ratio of average crater dimensions (such as depth or diameter) is on the order of the cube root of that number, or about 1.02. This means, in ram, that the basic characteristics of the regolith-mixing or reworking process as modeled for the Moon [e.g., Gault et al, 1974;McKay et al, 1974;Mendell and McKay, 1975] can be applied to Mercury with little concern for geometric differences. The second point builds upon the first: the ratios of melting to excavation indicate that twice as much melt will be produced by a single, average cratering event on Mercury when compared to the average impact on the Moon but that the amounts of material displaced by the two events will be virtually identical.…”

Section: A Detailed Comparison Of Regolith Mixing On the Moon Andmentioning

confidence: 99%

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Impact‐induced thermal effects in the lunar and Mercurian regoliths

1992

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While the Moon and Mercury are similar objects in a geomorphologic sense, they also possess important differences, particularly in the context of small‐scale impact phenomena. Not only is the surface of Mercury notably hotter than that of the Moon, but the impact flux is also more intense at Mercury due to higher impact velocities and a greater spatial density of micrometeoroids. By extrapolating the terrestrial micrometeoroid flux to the Moon and Mercury, it is found that the impact rate at Mercury is 5.5 times greater and the mean impact velocity more than 60 percent higher than at the Moon. A model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith. Although the surface temperature plays a role in determining the melt and vapor volumes, the difference in impact velocity appears to be markedly more important. “Average” craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size, because differences in the kinetic energy of the “average” impactors will be offset by the differences in gravitational acceleration. As a result, variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes. Each “average” impact on Mercury, however, will produce more than twice as much impact melt as its lunar counterpart, introducing more glass into the mercurian regolith. Although substantial quantities of impact vapor are produced on both planets, mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas; the resulting vapor coatings should be negligibly small for most purposes. A much larger agglutinate population should exist on Mercury, and individual agglutinates should be similar to those of the lunar highlands. Reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of Fe, perhaps similar to those of Apollo 16 light‐ and dark‐matrix breccias. Laboratory studies have demonstrated that, as the magnetic fractions (which are correlated with agglutinate abundances) of soils derived from these breccias increase, the differences in 0.565‐mm (visible light) reflectivity between the soils diminish. Should the regional variations in Fe‐content of the mercurian crust be similar to those of these Apollo 16 samples, then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface. At the same time, the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses, seriously attenuating the Fe2+ crystal‐field absorption near 0.9‐mm. Supporting this picture are the most recently published spectral observations of Mercury, which provide little or no evidence of such an absorption feature.

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Section: A Detailed Comparison Of Regolith Mixing On the Moon Andmentioning

confidence: 99%

“…[e.g.,Adams and McCord, 1971a;Pieters et al, 1985]. Nevertheless, the frequency of such impacts is so low relative to the rate of mixing and metamorphism at the surface that the eventual development of a "mature" surface layer is virtually guaranteed [cf Gault et al, 1974;Mendell and McKay, 1975;Morris, 1978a]…”

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confidence: 99%

Impact‐induced thermal effects in the lunar and Mercurian regoliths

1992

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“…Thus, if the ray deposit is more than 10 cm thick, it will darken at a rate independent of the original crater size. However, several effects will result in the more rapid loss of optical detectability of rays from smaller craters: (1) the more energetic secondary cratering from larger craters will expose more coarse lithic fragments [Thompson et al, 1981;Campbell et al, 1992], which acts to retard soil maturation as the large optically fresh particles are slowly pulverized [McKay et al, 1974;Mendell and 1 Ga. The craters were mapped as Copernican at least in part McKay, 1975]; (2) the volume and areal coverage of primary ray because of the presence of bright rays, but the rays are most apparent (or only apparent) over dark mare terrains.…”

Section: Introductionmentioning

confidence: 99%

“…However, several effects will result in the more rapid loss of optical detectability of rays from smaller craters: (1) the more energetic secondary cratering from larger craters will expose more coarse lithic fragments [Thompson et al, 1981;Campbell et al, 1992], which acts to retard soil maturation as the large optically fresh particles are slowly pulverized [McKay et al, 1974;Mendell and 1 Ga. The craters were mapped as Copernican at least in part McKay, 1975]; (2) the volume and areal coverage of primary ray because of the presence of bright rays, but the rays are most apparent (or only apparent) over dark mare terrains. The higher albedo of these rays relative to the substrate is primarily due to highlands materials excavated and deposited over the maria rather than being due to immature soils, as has been demonstrated in detail for Copernicus ] and ejecta will be greater from large craters, so the rays will be easier to detect away from secondary craters [Allen, 1977]; and (3) some relatively small rayed craters may be hidden within the bright rays of larger craters.…”

Section: Introductionmentioning

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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“…Recycling oflunar soils and soil grains is a well-documented process (e.g., McKay et al, 1974McKay et al, ,1977Mendell and McKay, 1975;Basu and Meinschein, 1976;Basu, 1990). Not only can fragments of older agglutinates be incorporated into newer agglutinates (Fig.…”

Section: Recyclingmentioning

confidence: 99%

Heterogeneous agglutinitic glass and the fusion of the finest fraction (F³) model

Basu

Wentworth

McKay

2002

Meteorit & Planetary Scien

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Abstract-Evidence in favor of the model fusion of the finest fraction (F3) for the origin of lunar agglutinitic glass has been accruing. They include (1) theoretical expectations that shock pulses should engulf and melt smaller grains more efficiently than larger grains, (2) experimental results of impact shock, albeit at lower than presumed hypervelocity impacts of micrometeorites on the lunar regolith, and (3) new analyses confirming previous results that average compositions of agglutinitic glass are biased towards that of the finest fraction of lunar soils from which they had formed. We add another reason in support of the F3 model. Finer grains of lunar soils are also much more abundant. Hence, electrostatic forces associated with the rotating terminator region bring the finest grains that are obviously much lighter than courser grains to the surface of the Moon. This further contributes to the preferential melting of the finest fraction upon micrometeoritic impacts. New backscattered electron imaging shows that agglutinitic glass is inhomogeneous at submicron scale. Composition ranges of agglutinitic glass are extreme and deviate from that of the finest fraction, even by more than an order of magnitude for some components. Additionally, we show how an ilmenite grain upon impact would produce Ti0 2-rich agglutinitic glass in complete disregard to the requirements of fusion of the finest fraction. We propose an addition to the F3 model to accommodate these observations (i. e., that micrometeorite impacts indiscriminately melt the immediate target regardless ofgrain size or grain composition). We, therefore, suggest that (1) agglutinitic glass is the sum of(a) the melt produced by the fusion of the finest fraction of lunar soils and (b) the microvolume of the indiscriminate target, which melts at high-shock pressures from micrometeoritic impacts, and that (2) because of the small volume of the melt and incorporating cold soil grains, the melt quenched so rapidly that it did not mix and homogenize to represent any preferential composition, for example, that of the finest fraction.

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A lunar soil evolution model

Cited by 18 publications

References 0 publications

Impact‐induced thermal effects in the lunar and Mercurian regoliths

Impact‐induced thermal effects in the lunar and Mercurian regoliths

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

Heterogeneous agglutinitic glass and the fusion of the finest fraction (F³) model

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A lunar soil evolution model

Cited by 18 publications

References 0 publications

Impact‐induced thermal effects in the lunar and Mercurian regoliths

Impact‐induced thermal effects in the lunar and Mercurian regoliths

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

Heterogeneous agglutinitic glass and the fusion of the finest fraction (F3) model

Contact Info

Product

Resources

About

Heterogeneous agglutinitic glass and the fusion of the finest fraction (F³) model