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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Thermal expansion and thermal stress in the moon and terrestrial planets - Clues to early thermal history

The paper discusses how features of the surface geology of the moon and also Mars and Mercury impose constraints on the volumetric expansion or contraction of a planet and consequently provide a test of thermal history models. The moon has changed very little in volume over the last 3.8 b.y. Thermal models satisfying this constraint involve early heating and perhaps melting of the outer 200 km of the moon and an initially cold interior. Mercury has contracted by about 2 km in radius since emplacement of its present surface, so core formation must predate that surface. A hot initial temperature distribution is implied.

Solomon, S. C.↗
NASA NTRS1977

Calculations of the moon's thermal history at different concentrations of radioactive elements, taking into account differentiation on melting

Calculations of the thermal history of the moon were done by solving the thermal conductivity equation for the case in which the heat sources are the long lived radioactive elements Th, U, and K-40. The concentrations of these elements were adjusted to give 4 variations of heat flow. Calculations indicated that the moon's interior was heated to melting during the first 0.7 to 2.3 x 10 to the 9th power years. The maximum fusion involved practically the entire moon to a distance from 15 to 45 km beneath the surface, and started 3.5 to 4.0 x 10 to the 9th power years ago, or 2.5 x 3.0 x 10 to the 9th power years ago and continued for 1 to 2 x 10 to the 9th power years. The moon today is cooling. The current thickness of the solid crust is from 150 to 200 km and the heat flow exceeds the stationary value 1.5 fold.

Ornatskaya, O. I.↗
NASA NTRS1977

Riddles about the origin and thermal history of the moon

Magmatic differentiation of the moon's interior, confirmed through calculations of thermal history, was studied. It appears that differentiation was a result of the moon's initial temperature whose origin remains unknown. In solving this problem, convective models of the moon were considered as well as a two layered differentiated model of the moon, operative over the past 3.5 billion years. The high content of long lived radioactive elements present was investigated in explaining the moon's current thermal properties. The controversy concerning the true nature of magmatic differentiation continues to be unsolved.

Levin, B. Y.↗
NASA NTRS1977

Early history of the moon: Implications of U-Th-Pb and Rb-Sr systematics

Anorthosite 60015 contains the lowest initial Sr-87/Sr-86 ratio yet reported for a lunar sample. The initial ratio is equal to that of the achondrite Angra dos Reis and slightly higher than the lowest measured Sr-87/Sr-86 ratio for an inclusion in the C3 carbonaceous chondrite Allende. The Pb-Pb ages of both Angra does Reis and Allende are 4.62 X 10 to the ninth power yr. Thus, the initial Sr/87/Sr-86 ratio found in lunar anorthosite 60015 strongly supports the hypothesis that the age of the Moon is about 4.65 b.y. The U-238/Pb-204 value estimated for the source of the excess lead in "orange soil" 74220 is approximately 35 and lower than the values estimated for the sources of KREEP (600-1000), high-K (300-600), and low-K (100-300) basalts. From these and other physical, chemical and petrographic results it was hypothesized that (1) the moon formed approximately 4.65 b.y. ago; (2) a global-scale gravitational differentiation occurred at the beginning of lunar history; and (3) the differentiation resulted in a radical chemical and mineralogical zoning in which the U-238/Pb-204 ratios increased toward the surface, with the exception of the low U-238/Pb-204 surficial anorthositic layer which "floated" at the beginning of the differentiation relative to the denser pyroxene-rich material.

Tatsumoto, M.↗
NASA NTRS1977

Lunar impact: A history of Project Ranger

Complete history of the Ranger project is provided as a tool for understanding the evolution and operational form of NASA's continuing progress of unmanned space exploration. Basic management techniques, flight operating procedures and technology for NASA's later unmanned lunar and planetary missions were reviewed. Methods for selecting experiments and integrating them with the spacecraft were also investigated.

Hall, R. C.↗
NASA NTRS1977

The Aristarchus-Harbinger region of the moon - Surface geology and history from recent remote-sensing observations

Photographic and remote sensing observations made from earth and Apollo orbiting spacecraft were used to study the Aristarchus Plateau-Montes Harbinger region. The appearance of the area is described, and a delineation of geologic map units and their stratigraphic relationships is presented. Physical and chemical properties of certain of the geologic units are deduced, and the interrelationships between materials of volcanic and impact origin, including the effects of excavation, redistribution, and mixing of previously deposited materials by younger impact craters, are discussed. A detailed geologic history of the region is developed. Attention is directed to the anomalous red dark mantle on the plateau; it is thought that this layer consists of fine-grained block-free material containing a relatively large fraction of orange glass, and that this layer is probably of pyroclastic origin, laid down at some time during the Imbrian period of mare flooding.

Zisk, S. H.↗
NASA NTRS1978

A general cratering-history model and its implications for the lunar highlands

Through analysis of a large number of Monte Carlo and Markov Chain simulations, a model for determining crater accumulation and crater obliteration histories has been derived. The model generally applies to populations of large craters. It predicts that the following relationships hold for subequilibrium-density crater populations: (1) the more negative the production function's exponent, alpha (N near D super alpha) the lower the crater density at which the population size-frequency distribution will significantly depart from its production function; (2) the more negative the production function's exponent, the less obliteration a crater population will sustain after a set number of impacts. Application of the model to the lunar highlands implies (1) the production function for the large craters is highly structured, resembling the observed size-frequency distribution and not the function N near D to the -2; (2) even the densely cratered highlands have not attained crater saturation or equilibrium. Direct simulations of the highlands' crater population supports the model's implications.

Woronow, A.↗
NASA NTRS1978

Some consequences of a liquid water saturated regolith in early Martian history

Flooding of low-lying areas of the Martian regolith may have occurred early in the planet's history when a comparatively dense primitive atmosphere existed. If this model is valid, the following are some pedogenic and mineralogical consequences to be expected. Fluctuation of the water table in response to any seasonal or longer term causes would have resulted in precipitation of ferric oxyhydroxides with the development of a vesicular duricrust (or hardpan). Disruption of such a crust by scarp undercutting or frost heaving accompanied by wind deflation of fines could account for the boulders visible on Utopia Planitia in the vicinity of the second Viking lander site. Laboratory and field evidence on earth suggests that under weakly oxidizing conditions lepidocrocite (rather than goethite) would have preferentially formed in the Martian regolith from the weathering of ferrous silicates, accompanied by montmorillonite, nontronite, and cronstedtite. Maghemite may have formed as a low-temperature dehydrate of lepidocrocite or directly from ferrous precursors.

Fuller, A. O.↗
NASA NTRS1977

Some constraints on the thermal history of the lunar magma ocean

If the accumulating evidence is accepted that the outer portion of the moon was molten for 100-200 million years, it is clear that a permanent insulating surface layer existed over nearly all of that epoch. Considerations of crustal stability against break-up and foundering lead to the view that this insulating blanket must have been an early-forming plagioclase-rich layer light enough to float on the hot magma. It is found that radiometric age-dating evidence implies a fairly specific history for the solidification of the lunar magma ocean. The possibility is anticipated that geochronological and petrological constraints will be sufficient to narrow the range of allowed geophysical and geochemical models. It is hoped that such a study will make it possible to deduce the original depth, and hence, the composition of the lunar magma ocean. If the moon accreted homogeneously, the composition of the magma ocean will also be that of the whole moon, and hence such models should allow estimation of the bulk lunar composition.

Herbert, F.↗
NASA NTRS1977

The history of the Apollo 17 Station 7 boulder

Rb-Sr and Sm-Nd methods were used to determine the age of the dark dikelets 77075 cutting the 4.36 b.y. noritic breccia 77215 of the Station 7 boulder of Apollo 17. A regression line corresponding to an age of 4.07 plus or minus 0.09 b.y. is obtained with an Rb-87 decay constant of 1.41 x 10 to the -11th/yr and an initial Sr-87/Sr-86 ratio of approximately 0.69918. It is noted that the intrusion age of the dikelets provides the most reliable criterion for determining the age of the entire boulder, i.e., the boulder is not an extension of 77115, which formed more recently. Attention is given to a generalized lunar history during the first 600 m.y.

Nakamura, N.↗
NASA NTRS1977

Pre-Imbrian history of the Fra Mauro region and Apollo 14 sample provenance

Pre-Imbrian impact structures in a large area surrounding the Apollo 14 site were identified in a study of the pre-Imbrian history of the Fra Mauro region. Calculations suggest that a total ejecta thickness of over 1700 m could have accumulated during Phase I (time prior to the Imbrium event) in the area of the ridge on which the Cone crater later formed. The majority (53%) of the ejecta at the site just prior to the Imbrium event was contributed by the numerous large Phase IB and IC craters in the vicinity and not by the lunar basins. Evidence exists for extensive pre-Imbrian volcanic activity in the Fra Mauro region. Early KREEP volcanic deposits may have existed in the target sites of many Phase IB and IC craters and would have been incorporated into their ejecta.

Hawke, B. R.↗
NASA NTRS1977

Irradiation history of lunar cores and the development of the regolith

Detailed studies by the nuclear particle track method of lunar core sections 70009, 70008, 60007, 60010, and 60009 indicate that the irradiation and depositional histories of individual lunar cores vary greatly. The presence of layers a few cm thick which have remained largely undisturbed for periods ranging from 1 to 100 m.y. is a common feature although the development of the regolith usually proceeds through the accumulation of smaller increments of heavily irradiated material that do not result in distinct layers. Typical accumulation rates are on the order of 1 cm/m.y.

Crozaz, G.↗
NASA NTRS1977

Cosmic-ray exposure history at Taurus-Littrow

Recent surface history at Taurus-Littrow is dominated by emplacement of the Central Cluster and Bright Mantle morphological units, both believed to have resulted from arrival of ejecta from a large primary crater, probably Tycho. This paper reports new noble gas data for eight Apollo 17 rocks. Kr-81 - Kr cosmic ray exposure ages for these rocks affirm the observation of a pronounced grouping of ages, reinforcing the photogeologic evidence for the site-wide nature of the Central Cluster event. The consequences of post-cratering shielding changes are considered and it is concluded that the differences can reasonably be attributed to these changes, particularly because of the greater likelihood of rollover and impact fragmentation of the relatively smaller rocks from which most age data have been obtained. These considerations also lead to a more refined age estimate of 109 plus or minus 4 m.y. for Central Cluster, the Bright Mantle, and Tycho.

Drozd, R. J.↗
NASA NTRS1977

Nitrogen isotopes in lunar soils as a measure of cosmic-ray exposure and regolith history

Previous studies have shown that the bulk of the nitrogen in soils has been implanted by the solar wind, that the N-15/N-14 ratio of the implanted nitrogen has apparently increased with time, and that both soils and rocks contain a nitrogen component greatly enriched in N-15, relative to natural abundance ratios, due to cosmic-ray spallation. An investigation was, therefore, conducted to test the feasibility of using spallation-produced N-15 for determining cosmic-ray exposure ages. Samples from several depths in the Apollo 15 deep drill core were analyzed. The data obtained have also been evaluated with regard to possible models for the prior history of the material now in the Apollo 15 core. In addition, analyses have been performed of several other soil samples considered for various reasons to be of particular interest, such as orange soil 74220 and its companion 74240, Apollo 16 drill core sample 60002, and the apparently peculiar fillet soil 67461. Wherever possible, analyses were carried out by step-wise heating rather than by total pyrolysis. On the basis of the results of the investigation it is concluded that nitrogen isotope ratio determinations provide a usable method for determining cosmic-ray exposures for soils.

Becker, R. H.↗
NASA NTRS1977

Fourier analysis of planimetric lunar crater shape - Possible guide to impact history and lunar geology

If the lithology of lunar crust influences impact crater morphology, a method of analysis that is sensitive to small-scale changes in crater shape is required. In the present paper, it is shown that Fourier analysis in closed form can provide detailed information regarding planimetric crater shape. Preliminary analysis of the rim crest outline of 247 nearside lunar craters (larger than 18 km in diam) led to the following information: Imbrian and pre-Imbrian craters are more elongate than younger craters, possibly as a result of widespread crustal deformation early in the moon's history. Crater size does not affect the planimetric shape of craters. Highland craters are less circular than mare craters, probably due to the greater structural and lithologic complexity of the highland crust. Craters comprising each shape family of the eleventh harmonic typically are located in the same general geographic region of the moon.

Eppler, D. T.↗
NASA NTRS1975

Experimental modeling of the cooling history of Apollo 12 olivine basalts

An analog of the Apollo 12 olivine vitrophyres has been crystallized in a 1-atm gas-mixing furnace at cooling rates ranging between 1250 and 0.7 C/hr and isothermally at degrees of supercooling ranging from 10 C to 325 C. Mineral chemistry, crystal shapes, grain sizes and textures are systematically related to cooling rate and degree of supercooling. At linear cooling rates not exceeding 40 C/hr the texture is porphyritic - large olivine crystals are set in a groundmass of finer-grained pyroxene, plagioclase, and ilmenite; a later generation of olivine never crystallizes. There are three shapes of olivine crystals in the Apollo 12 olivine vitrophyres: glomerocrysts of subhedral crystals, large subequant skeletons, and highly elongate skeletons. These result from three generations of nucleation and a two-stage cooling history - a slow preeruption stage and a rapid continuously increasing posteruption stage. It seems likely that the Apollo 12 olivine basalt magmas were erupted with olivine crystals in suspension. The nucleation temperature of olivine in cooling-rate experiments is dependent on the experimental technique, and hence results of cooling experiments should be applied with caution.

Donaldson, C. H.↗
NASA NTRS1975

A physical and chemical model of early lunar history

A 'cool' thermal model of the moon's early history is discussed in terms of lunar petrology. Heat from the totally molten outer half of the moon's volume was, according to the model, lost to space and to the lunar interior, so that, barring additions of heat from external sources, all petrogenesis operating exclusively on material of the initially totally molten zone must have occured in an environment of decreasing temperatures. Mare basalts would result from hybridization by migration, mixing, and reequilibration of a variety of intercumulus liquids. Evidence is considered for the layered structure and a significant structural boundary that should result from differentiation of the approximately 350-km-thick initially totally molten zone. Magnetization of lunar rocks is considered.

Hubbard, N. J.↗