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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Magma production and migration within the moon

Partial melting is likely to have occurred throughout much of the moon due to heating during accretion and the volumetric heating of radioactive isotopes. Important problems that have received relatively little attention concern the migration of the resulting magmas to form surface or near surface volcanic rock. In the paper the basic mechanism for the migration of the magma through the lunar asthenosphere is considered. A porous flow model is proposed. The magma behaves like a liquid flowing through a porous matrix. The volume fraction of liquid present determines the saturated porosity. The differential buoyancy of the magma drives it upwards. It is shown that the per cent partial melt in the lunar interior will only slightly exceed that required to provide interconnecting porosity. Assuming that the radioactive isotopes are preferentially segregated into the magma, the time dependence of the partial melting of the lunar interior is found. It is shown that the total degree of partial melting of the deep lunar interior is likely to be between five and ten per cent.

Turcotte, D. L.↗
NASA NTRS1978

Transport of terrestrial atmospheric gases to the moon

The suprathermal Ion Detector Experiment instruments on the lunar surface have identified fluxes of ions which may be different from the solar wind both in elemental and in isotopic abundances. At present, only O/+/ is (tentatively) identified, but the mechanism operates to produce ions at the moon which have their origin in the earth's atmosphere. Consequently, the 'solar wind' component of the surface-correlated gases is effectively a combination of terrestrial atmospheric ions and the actual solar wind. The results differ from solar wind results if the terrestrial ion abundances strongly differ from those of the solar wind.

Hills, H. K.↗
NASA NTRS1978

Interpretation of ground-based microwave measurements of the moon using a detailed regolith properties model

A detailed model for the regolith's thermophysical and microwave properties has been used for the interpretation of ground-based measurements of the moon's microwave brightness temperature variation with lunar phase and changes during eclipses. The ground-based measurements include some crucial new lunation variation observations at 2.8, 6.0 and 13.1 cm. The many parameters in the regolith properties model were assigned values based on a careful review of Apollo in situ and lab sample measurements of thermophysical and electrical properties. The first identification of a wavelength-dependent component of scattering is reported.

Gary, B. L.↗
NASA NTRS1978

Mare volcanism in the Herigonius region of the moon

The paper considers the area in the vicinity of the crater Herigonius. This area contains numerous sinuous rilles, craters with irregular planimetric form, possible pyroclastic cones, and other features of probable volcanic origin, and appears to be the vent region that supplied lavas both northward to Oceanus Procellarum and southward to the Humorum basin. The approach used involves photogeologic interpretation of surface features and mapping of mare units to derive a regional stratigraphic sequence. The sequence of mare volcanism provides insight into the complex emplacement of lunar lavas and the general volcanic history of the moon.

Greeley, R.↗
NASA NTRS1978

Yield strengths of flows on the earth, Mars, and moon

Dimensions of flows on the earth, Mars, and moon and their topographic gradients obtained from remote measurements are used to calculate yield strengths with a view to explore the validity of the Bingham plastic model and determine whether there is a relation between yield strengths and silica contents. Other factors are considered such as the vagaries of natural phenomena that might contribute to erroneous interpretations and measurements. Comparison of yield strengths of Martian and lunar flows with terrestrial flows suggests that the Martian and lunar flows are more akin to terrestrial basalts than they are to terrestrial andesites, trachytes, and rhyolites.

Moore, H. J.↗
NASA NTRS1978

Age of graben systems on the moon

The study focuses on the time of formation of the graben. An attempt is made to determine whether the graben are restricted to geologic units of certain ages, and whether and at what time graben formation ceased. It is shown that (1) most preserved graben formed considerably later than the impacts that formed the basins; (2) graben are faults that are reactivated along older basin concentric and radial structures and lunar grid directions; (3) graben formation ceased about 3.6 + or - 0.2 b.y. ago; and (4) graben formation reflects a tensile stress fields that obtained during part of early lunar history. Other features of graben systems on the moon are also identified.

Lucchitta, B. K.↗
NASA NTRS1978

The nature of isostasy on the moon - How big a Pratt-fall for Airy models

The correlation between topographic elevation and the major element chemistry of the lunar surface in non-mare regions suggest that a Pratt-type isostatic mechanism may be important in the lunar highlands. Pratt isostasy involves compensation of greater elevation by lower crustal density. Computation of the bulk density from surface chemistry and normative mineralogy, followed by comparisons between calculated density and surface height, is suggested as a means of testing the applicability of the Pratt isostatic model to the moon. A Pratt-type lunar crustal model requires much smaller variations in lunar crustal thickness than those necessitated by a constant-density (Airy) isostatic model. Mechanisms to produce a crust regionally heterogeneous in composition early in lunar differentiation are also required for Pratt isostasy.

Solomon, S. C.↗
NASA NTRS1978

Energy and mass distributions of impact ejecta blankets on the moon and Mercury

The paper applies previously calculated impact-induced flow fields (O'Keefe and Ahrens, 1977) resulting from interaction of 5-cm radius gabbroic anorthosite impactor with a half-space of the same material, at various velocities, to obtain mass and energy ejecta distributions. Whereas earlier results described the ejecta distribution from a 15 km/s impact of an iron object on the moon in terms of mass vs. distance, the present results describe, at a given distance from the impact, the energy content as a function of depth, i.e., the thermal structure of ejecta blankets. Pertinent computational methods are included, and several tables and plots supplement the text.

Ahrens, T. J.↗
NASA NTRS1979

Collisional and dynamical processes in moon and planet formation

The collisional and dynamical processes in moon and planet formation are discussed. A hydrodynamic code of collision calculations, the orbital element changes due to gravitational scattering, a validation of the mass shifting algorithm, a theory of rotations, and the origin of asteroids are studied. A numerical model of planet growth is discussed and a methodology to evaluate the rate at which megaregolith increases its depth as a function of total accumulate number of impacts on an initially smooth, coherent surface is described.

Source record↗
NASA NTRS1979

Tenth anniversary of Apollo 11 moon landing

The proceedings from the tenth anniversary of the Apollo 11 Moon landing are presented. Future direction of the space programs and space exploration are discussed.

Source record↗
NASA NTRS1979

Are early magnesium-rich basalts widespread on the moon

Orbital X-ray data indicate that high-magnesium material systematically occurs along mare/terra boundaries in all the lunar nearside basins for which there is orbital X-ray coverage. These peripheral units appear to represent the earliest stages of volcanism within each of the basins, although they were not necessarily emplaced at the same time in lunar history. High-magnesium subsurface layers excavated by post-mare impact craters in central Mare Crisium and Mare Fecunditatis suggest that the peripheral units are the only visible edges of a basin-wide basalt layer, largely buried by younger less-magnesian flows. This evidence suggests that early magnesium-rich mare basalts are widespread on the moon and that their volumes may be greatly underestimated. Abundant early mare deposits of this type would place severe constraints on models of mare basalt petrogenesis.

Andre, C. G.↗
NASA NTRS1979

Parameterized convection within the moon and the terrestrial planets

For a fluid layer or a self-gravitating fluid sphere uniformly heated from within, the internal temperature can be parameterized in terms of the appropriate Rayleigh number. The heat generation term includes both radioactive heat release and transient heating or cooling. This parameterization has been verified by comparisons with laboratory experiments. Thermal history calculations have been carried out for the earth, Venus, Mars, Mercury, and the moon. The results for the earth and Venus indicate that two scales of convection are occurring, one including the surface plates and the second occurring beneath the surface plates. In all cases the present heat flows are between seven and twelve per cent greater than the values obtained assuming a steady state balance between heat flow and internal heat generation.

Turcotte, D. L.↗
NASA NTRS1979

The bounds of the heat production rate within the moon

A new approach is proposed to the evaluation of the lower and upper bounds of the global heat production rate within planetary interiors. The approach is based on the relationship between the internal energy change and the volume change of a planetary object. For illustration, the approach is applied to the moon. Using an average global surface heat flux of 18 erg/sq cm-sec, and assuming constancy of the lunar radius during the past 3.2 billion years. the lunar heat release within the past 3.2 billion years is estimated at (30 to 40) x 10 to the tenth erg/cu cm. This is equivalent to the present day uranium concentration of 35 to 50 ppb provided the radiogenic isotopes are of the same proportion as that given by Toksoz et al. (1978).

Hsui, A. T.↗
NASA NTRS1980

Cometary collisions on the moon and Mercury

Unusual swirl patterns of bright and dark material on the moon and Mercury are proposed to be remnants of collisions with gas/dust-rich regions within a cometary coma. This interpretation provides important new clues for understanding cometary fine structure, impact effects of low-density material, and the origin of certain pronounced magnetic anomalies.

Schultz, P. H.↗
NASA NTRS1980

Whole planet cooling and the radiogenic heat source contents of the earth and moon

Thermal evolution models based on subsolidus whole mantle convection which indicate that the surface heat flows of the earth and the moon do not necessarily provide good measures of the total amounts of radioactives in these bodies have been constructed. These models assume an initially hot state, but with a wide variety of choices for the parameters characterizing the rheology and convective vigor. All models are constrained to be consistent with present-day surface heat fluxes, and many of the terrestrial models are consistent with the mantle viscosities indicated by postglacial rebound. In the lunar models, heat generation is typically only 70-80% of the surface heat flow, even with allowance for the strong near-surface enhancement of radioactives. Despite the simplicity of these models, the persistence of a significant difference between heat generation and heat output indicates that this difference is real and should be incorporated in geochemical modeling of planets.

Schubert, G.↗
NASA NTRS1980

The moons of Mars

The physical properties, surface morphology, crater ejecta, and origin of Mars' moons Phobos and Deimos are considered in light of the intensive research done through the Mariner and Viking missions. Particular attention is given to orbits, secular acceleration and tides, photometric properties and phase curves, crater densities, grooves on Phobos, cratering mechanics, and dust belts.

Veverka, J.↗
NASA NTRS1980

Iron and titanium distribution on the moon from orbital gamma ray spectrometry with implications for crustal evolutionary models

A set of Fe and Ti maps and regional values are obtained from the Apollo 15 and 16 orbital gamma ray data by energy band analysis. High-Ti basalts predominate the early and late stages of mare volcanism with high-Fe basaltic volcanism in the interim. The first evidence of a high-Ti-KREEP basalt association is found in the Aristarchus region. A N-S asymmetry for Fe and Ti in the east limb and farside highlands complicates the E-W asymmetry for Th but substantiates crustal inhomogeneity. The observed crustal inhomogeneity adds an additional objection to the primitive source model for crustal evolution. The high-Ti-KREEP basalt association and the general trend of decreasing mare basalt Ti with time lend support to the cumulate source model; however, this model cannot account for young, high-Ti maria. The dynamic assimilation model better accounts for chemical variations observed on the moon.

Davis, P. A., Jr.↗