Engineering topics

Minear, J. W.

Publications and source records attributed to Minear, J. W..

7 records

NASA NTRS1980

The lunar magma ocean - A transient lunar phenomenon

The time required for the solidification of a lunar magma ocean is considered. In the absence of a thermal boundary crust, heat loss is by radiation and the ocean will solidify in a few decades. However, only a few millimeters of crust would effectively limit radiation. The current investigation has the objective to present estimates of conduction boundary (crust) thickness based on several models of the mechanism of crustal formation. Three different models for estimating conduction boundary layer thickness are discussed. They are based on the formation of a chill margin, a plagioclase flotation layer, and a layer which is continually destroyed by meteorite impacts and regrows by conductive heat loss. Based on these models, the maximum solidification time for a 200 km thick ocean is about 100 million years. A more probable solidification time based on a plagioclase flotation crust model is about 60 million years.

Minear, J. W.↗

NASA NTRS1979

Consideration of sample return and the exploration strategy for Mars

The scientific rationale and requirements for a Mars surface sample return were examined and the experience gained from the analysis and study of the returned lunar samples were incorporated into the science requirements and engineering design for the Mars sample return mission. The necessary data sets for characterizing Mars are presented. If further analyses of surface samples are to be made, the best available method is for the analysis to be conducted in terrestrial laboratories.

Bogard, D. C.↗

NASA NTRS1978

Crystallization of a lunar magma ocean

The results of applying the presently most detailed thermal model to the cooling, crystallization and differentiation of a lunar magma ocean are used to delineate its general features, i.e., those features that are model independent within reasonable variations in ocean characteristics. Two primitive lunar compositions are used to illustrate the effect of different compositions and phase equilibria on the solidification time and mineralogy of magma oceans. The magma ocean thermal model led to some inferences about the thermal evolution of the outer portion of the moon modeled as isolated magma pods rather than as a magma ocean.

Minear, J. W.↗

NASA NTRS1976

Lunar mare basalts - Conference summary

Compositionally, lunar mare basalts are similar to some very young subalkaline basalts from terrestrial mid-ocean ridges and to very old pods of basaltic material incorporated into ancient metamorphic rocks. Basalt flows in Mare Imbrium are considered, taking into account the results of orbital gamma ray spectroscopic studies. The results of the analyses of lunar samples obtained from the Apollo missions are evaluated and various models are discussed in connection with an interpretation of the observed conditions.

Merrill, B.↗

NASA NTRS1976

Petrogenesis in a modestly endowed moon

Four lines of recent evidence show that the moon is more modestly endowed in refractory elements and heat sources than previously thought. However, even this reduced endowment is adequate for the genesis of known lunar rock types. The thickness and nature of the initially molten zone and the structure of the crust and the lithosphere produced from it are the major uncertainties in models of lunar petrogenesis.

Hubbard, N. J.↗

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.↗

NASA NTRS1972

Thermal evolution of the moon.

The thermal history and current state of the lunar interior are investigated using constraints imposed by recent geological and physical data. Theoretical temperature models are computed taking into account different initial conditions, heat sources, differentiation and simulated convection. To account for the early formation of the lunar highlands, the time duration of magmatism and present-day temperatures estimated from lunar electrical conductivity profiles, it is necessary to restrict initial temperatures and abundances of radioactive elements. Successful models require that the outer half of the moon initially heated to melting temperatures, probably due to rapid accretion. Differentiation of radioactive heat sources toward the lunar surface occurred during the first 1.6 billion years. Temperatures in the outer 500 km are currently low, while the deep interior (radius less than 700 to 1000 km) is warmer than 1000 C, and is of primordial material.

Toksoz, M. N.↗