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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Thermodynamic history of a solar active region observed in X-rays

The structure and energy content of an active coronal volume during its early history are investigated using soft X-ray images secured with the glancing-incidence telescope on Skylab. During the late stages of emerging-flux-region activity, the maximum temperatures exceeded 6.5 million K. At that time, the temporal rate of change in thermal energy content was about 10 to the 25th power ergs/s and was comparable to the rate of energy loss by radiation. Fluctuations in the energy content of the X-ray source region imply that this coronal active region was probably not in energy equilibrium during the five days of observation.

Teske, R. G.↗
NASA NTRS1977

A calculation of Saturn's gravitational contraction history

A gravitational-contraction history is calculated for a homogeneous quasi-equilibrium Saturn model of solar composition without a rock-ice core and without allowance for the possible separation of hydrogen and helium. The calculations begin at the time when Saturn's radius was ten times its current value, and the subsequent gravitational contraction is followed for 4.5 billion years. The results obtained are given in terms of the path of the evolving model on the H-R diagram, the variation of central temperature with central density, the time variation of radius and internal luminosity, and the energy changes that take place during the evolution. These results are compared with those of similar calculations for Jupiter, and the internal structure of the evolutionary models is examined in detail. The Saturn calculations yield a radius at the current epoch that is 9% larger than the observed value and an excess luminosity comparable to that observed. It is noted that an inhomogeneous model containing a solar-mix envelope and a central rocky core has a radius equal to the observed value.

Pollack, J. B.↗
NASA NTRS1977

The record of solar and galactic radiations in the ancient lunar regolith and their implications for the early history of the sun and moon

The paper reviews research into the nature and history of the lunar environment, as recorded in rocks and core samples, performed by studying effects produced by the energetic nuclear particles constituting the solar wind, solar flares, and galactic cosmic rays. Results obtained with lunar rocks are discussed which suggest a remarkable constancy of the lunar environment at least over the last several million years. Analyses of lunar core samples are examined which indicate an apparent secular change in the N-15/N-14 ratio with time in solar-wind-related nitrogen, possibly due to greatly enhanced solar flare activity in the past. Lunar and meteoritic breccias are proposed as obvious candidates for extending the radiation record much further back in time, perhaps even close to the beginning of the solar system.

Grozaz, G.↗
NASA NTRS1976

Did mare-type volcanism commence early in lunar history

The bombardment history of the moon precludes the presence of abundant volcanic fragments and flows much older than 4.0 b.y. It is maintained, therefore, that the negative evidence that has led to the assumption that mare-basalt volcanism did not commence until about 4.0 b.y. or later does not in any way preclude such earlier volcanism. Fragments of mare-like volcanic rock in breccias older than 3.95-4.0 b.y. attest to the presence of mare-related volcanism during the intense bombardment episode.

Ryder, G.↗
NASA NTRS1976

History and genesis of lunar troctolite 76535 or: How old is old

The history of lunar troctolite 76535 was investigated on the basis of information from the Sm-147-Nd-143 mineral isochron age, the Nd-143 evolution, extinct Pu-224, the Kr-81-Kr exposure age and the cosmic ray exposure record. It was found that the troctolite minerals last equilibrated 4.26 plus or minus 0.06 AE ago and that the Sm-Nd system became closed at this time. The rock remained at temperatures where the loss of radiogenic Ar-40 was small.

Lugmair, G. W.↗
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.↗