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Morrison, D. A.

Publications and source records attributed to Morrison, D. A..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Geology of the Luna 24 landing site

The Soviet spacecraft Luna 24 landed at the southeast edge of Mare Crisium on the moon on August 18, 1976. A 160 cm core with a diameter of 8 mm was drilled, extracted, and returned to earth by the spacecraft. A description is presented of the geologic setting at the Luna 24 landing site to provide background information for the study of Luna 24 samples. Interpretations of spectral reflectance data suggest that the Luna 24 landing area is similar in TiO2 content to Oceanus Procellarum. Mare Crisium fills the interior of a circular multiringed impact structure in the eastern hemisphere of the moon. Stratigraphic units within Mare Crisium consist of mare materials and postmare deposits. Aspects of local stratigraphy are discussed, taking into account ray material and mare material. In the vicinity of the Luna 24 landing site, the terrain may be divided into four areas on the basis of topography.

Butler, P., Jr.↗
NASA NTRS1976

The size frequency distribution and rate of production of microcraters

The paper contends that lunar crater size distributions vary to a degree that cannot be explained by variations in lunar surface orientation of the crater detectors or changes in micrometeoroid flux. In an attempt to investigate this size frequency distribution, a flux of micrometeoroid particles producing 0.1 micron diameter craters of approximately 300/sq cm/steradian/yr was obtained. No anisotropy was observed in the 0.1 micron flux between the ecliptic plane and the normal in the direction of lunar north.

Morrison, D. A.↗
NASA NTRS1976

Stratigraphy in Apollo 16 drill section 60002

Contacts in drill stem 60002 which indicate layers at least several centimeters thick and with one firm age of about 2.5 x 10 to the 7th yr are observed on the basis of characteristic patterns of track density variation with depth from the contact. The patterns can be observed primarily because the drill stem has a large immature component (path II soils).

Blanford, G. E.↗
NASA NTRS1975

Studies of solar flares and impact craters in partially protected crystals

Solar-flare track gradients and microcrater densities were determined in two lunar rocks, and it was found that approximately 900 craters greater than or equal to 0.1 microns in diameter and between 10 and 15 times 10 to the minus sixth craters greater than or equal to 500 microns central pit diameter are produced per sq cm per yr per 2-pi steradians on the moon. There is no evidence for a change in the flux of particles producing submicron craters in the last 1,000,000 years. No anisotropy was found between lunar north and the plane of the ecliptic in the directional flux distribution of micrometeoroids producing submicron craters. In contrast to data reported by other investigators, the ratio of solar-flare track densities at 100-micron depth to the abundance of 0.1-micron craters/sq cm is determined to be approximately one for all samples studied.

Morrison, D. A.↗
NASA NTRS1975

Surface exposure history of individual crystals in the lunar regolith

The paper reports measurements of solar-flare tracks, microcraters, and glass accretionary particles in crystals from several mature soil samples and from different levels of the Apollo 15 and 16 deep drill stems. Although almost every crystal appears to have been at (or very near) the surface of the moon, the crater data indicate that typical grains are exposed to free space for only 1000-10,000 years. Neither total track densities nor track gradients are correlated with the presence of or absence of crater surfaces. Also considered is the use of cratered crystals in assessing the nature of surface changes produced by various treatments employed to study 'surface' effects.

Poupeau, G.↗
NASA NTRS1975

Long-term differential energy spectrum for solar-flare iron-group particles

A long-term solar-flare differential energy spectrum for iron-group nuclei from approximately 0.1 to approximately 600 MeV/amu is derived from track density profile measurements in sample 64455 and sample 68815. Measurements from uneroded surfaces were obtained from quench crystals of plagioclase in 64455, and a Kr-81/Kr method indicates that the exposure age of this sample is 2,010,000 yrs. The power laws which best fit the normalized track density data are reported; the energy spectrum consists of two power law curves smoothly joined together which in turn are smoothly connected to a modulated galactic cosmic-ray spectrum. Standard track production versus depth profiles can be used to determine solar-flare track exposure ages and erosion rates for lunar samples.

Blanford, G. E.↗
NASA NTRS1974

The micrometeoroid complex and evolution of the lunar regolith

The interaction of the micrometeoroid complex with the lunar surface is evidenced by numerous glass-lined microcraters on virtually every lunar surface exposed to space. Such craters range in size from less than .1 micron to approximately 2 sq cm diameter. Using small scale laboratory cratering experiments for calibration, the observed crater-sized frequency distributions may be converted into micrometeoroid mass distributions. These lunar mass distributions are in essential agreement with satellite data. Some physical properties of micrometeoroids may be deduced by comparing lunar crater geometries with those obtained in laboratory experiments. The proponderance of circular outlines of lunar microcraters necessitates equidimensional, if not spherical, micrometeoroids.

Hoerz, F.↗
NASA NTRS1974

Micrometeoroids and lunar rocks

Description of present concepts of the lunar micrometeoroid flux as deduced from microcrater observations on lunar rocks and available laboratory simulations with smooth glassy surfaces. Results examined include factors governing microcrater morphology, size frequency distribution, and correlation of lunar rock surface exposure ages with absolute crater number densities.

Hoerz, F.↗
NASA NTRS1974

Lunar surface phenomena - Solar flare track gradients, microcraters, and accretionary particles

Data are presented concerning the energy spectra of solar flare particles and the distribution of particles producing submicron diameter craters. Processes which alter the albedo and possibly the chemistry of exposed lunar surfaces are also considered. Measurements are reported of solar flare track gradients in rock 64455 which is sufficiently young to have uneroded surfaces on its sides. Attention is also given to accretionary particles adhering to host surfaces, microcraters on soil particles, and microcraters on the oriented surfaces of sample 76015 from a boulder at Station 6 of the Apollo 17 site.

Blanford, G. E.↗
NASA NTRS1973

Microcraters on Apollo 15 and 16 rocks

Microcrater frequency distributions, determined for 11 Apollo 16 rocks and three Apollo 15 rocks, fall into four categories. Category 1 rocks (68415, 68416, 62235) are angular, cratered on one side only, and have moderate crater densities. Category 2 rocks (60016, 66075, 61175) are subrounded, cratered on all sides, and have distributions suggestive of the steady state. Category 3 rocks (61015, 62295) are subangular and cratered on only one side, but the crater frequency distributions have some of the characteristics of category 2 rocks. Category 4 rocks (15015, 15017, 15076, 60335) are angular, cratered on only one side, and have moderated to very low crater densities. The crater frequency distributions of categories 1 and 4 have properties indicating the possibility of estimating the time they were exposed to micrometeor bombardment. Category 1 rocks appear to have been exposed for 2 to 3 m.y. These rocks, particularly 68415, 68416, and 69935, may be ejecta from South Ray Crater, indicating an age of 2 to 3 m.y. for South Ray Crater. Category 4 rocks have been exposed for much shorter periods.

Morrison, D. A.↗
NASA NTRS1973

Crater populations on lunar rocks

Approximately 10,000 microcraters were investigated using binocular microscope techniques on fifteen Apollo 16 rocks: crystalline rocks 60315, 60335, 61156, 62235, 62295, and 68415; breccias 60016, 61015, 61175, 66075, and 69935; and glass surfaces 60015, 60095, 60135, and 64455. Diameter measurements of the central glass-lined pits and surrounding spall zones were made. Ratios of spall to pit diameters may range from 3.0 to 4.5 for different rock surfaces. Crater size distributions obtained for production surfaces confirm and extend to larger crater sizes data published previously. The crater size distribution on lunar rocks in the pit diameter range, 10 to 1000 microns, is shown to depend on the average angle of impact which is a function of the exposure geometry. In contrast to results of earlier studies, a wide range of crater densities was observed on relatively heavily cratered surfaces.

Neukum, G.↗
NASA NTRS1972

Phenocryst fabric in lunar basalt sample 12052 from the Ocean of Storms.

Pyroxene phenocrysts in Apollo 12 sample 12052, a porphyritic basalt, have a weak, planar preferred orientation and a lineation as determined by crystal-elongation measurements and universal-stage measurements in orthogonal thin sections. The structures are probably the result of laminar flow. Numerous vugs and the flow foliation in sample 12052 suggest crystallization as a surface flow or a near-surface sill. Flowage appears to have ceased by the time of crystallization of the variolitic groundmass of the sample. The fabric data suggest a two-stage crystallization of sample 12052.

Greenwood, W. R.↗
NASA NTRS1972

The surface orientation of some Apollo 14 rocks.

Detailed stereomicroscopic studies of the distribution of microcraters, soil covers, and glass coatings were performed to reconstruct the most recent surface orientations of selected Apollo 14 rocks. Surface orientations could be established for rocks 14053, 14073, 14301, 14303, 14307, 14310, and 14311 (which includes rock 14308). A tentative orientation of rock 14055 is suggested, and comments concerning the surface history of rocks 14302, 14305, and 14318 are presented. The examination of rocks 14066, 14306, and 14321 indicates that these specimens have complicated surface histories that prevent reconstruction of their orientation by the criteria that were established in these stereomicroscopic studies.

Hoerz, F.↗
NASA NTRS1972

Vapor phase crystallization in Apollo 14 breccia.

The vugs contained in many of the highly recrystallized breccias from Apollo 14 are discussed, along with the well-developed crystals of plagioclase, pyroxene, ilmenite, apatite, whitlockite, iron, nickel-iron, and troilite that extend from the vug walls and bridge open spaces. These crystals are interpreted as having formed by deposition from a hot vapor containing oxides, halides, sulfides, alkali metals, iron and possibly other chemical species. The hot vapor was associated with the thermal metamorphism and subsequent cooling of the Fra Mauro formation after it had been deposited as an ejecta blanket by the Imbrian impact.

Mckay, D. S.↗
NASA NTRS1972

Apollo 14 soils - Size distribution and particle types.

Particle size characteristics are discussed together with particle types, abundances, variation in the soils, questions of soil maturity, coarse fines, and ropy glasses. It is found that agglutinates are formed primarily by micrometeorite impact into lunar soil. Agglutinates appear to be the major particle type now being formed on the lunar surface. Agglutinate content of a soil increases with particle track densities and with surface exposure time.

Mckay, D. S.↗
NASA NTRS1972

Microcraters on lunar rocks.

Microcrater frequency distributions have been obtained for nine Apollo rocks and an exterior chip of an Apollo 12 rock. The frequency distributions indicate that five of the Apollo 14 rocks were tumbled more than once exposing different rock faces whereas four were not tumbled and represent a single exposure interval. The cumulative frequency of craters per square centimeter was extended below optical resolution limits using a SEM scan of an exterior chip of breccia 12073. No craters with central pit diameters less than 15 microns were seen in a total area of 0.44 sq cm. A detailed SEM scan of crystal faces and glassy crater liners revealed no microcraters equal to or larger than the resolution limit of 5 microns. An upper limit of 170 craters per sq cm with central pit diameters larger than 5 microns was set. The slope of the cumulative frequency curve for craters with central pit diameters less than about 75 microns is less than that obtained by other workers.

Morrison, D. A.↗