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At least 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Early chemical history of the solar system

By using equilibrium thermodynamics, the sequence of condensation of mineral phases from a cooling nebula of solar composition has been calculated. The theoretical models suggest that the chemistry and mineralogy of Ca-Al-rich inclusions in C2 and C3 chondrites were established during condensation at temperatures above 1300 K. Fractionation of such inclusions is necessary to account for the refractory element depletions of ordinary and enstatite chondrites relative to the carbonaceous chondrites. The metal-silicate fractionation in ordinary chondrites took place in the nebula at a temperature below 1000 K and at .00001 atm total pressure. The volatile element depletion of C2 and C3 chondrites relative to C1 chondrites took place during chondrule formation: the most volatile elements are depleted in ordinary chondrites because they accreted before these elements were totally condensed.

Grossman, L.↗
NASA NTRS1973

Crystallization history of metal particles in Apollo 16 rake samples

Electron microprobe analyses for Fe, Co, Ni, S, and P have been carried out on the metal and associated troilite, schreibersite, and rare cohenite in the Apollo 16 rake samples from Stations 1, 4, and 13. The Co/Ni ratios of most of the metal are within the limits of meteoritic metal as defined by Goldstein and Yakowitz (1971). The large abundance of schreibersite in all of the lithic types except the poikilitic rocks suggests that much of it may be of lunar origin. The near-absence of schreibersite in the poikilitic rocks may be a result of P diffusion from the metal to the surrounding silicate at low temperature. Application of the compositional data for the coexisting metal-schreibersite pairs to isotherms in the system Fe-Ni-P indicates a sequence of progressively lower temperatures of equilibration (and probably a corresponding sequence of slower cooling rates) of these phases from the devitrified glasses, to the mesostasis-rich rocks, to the diabases, to the poikilitic rocks.

Gooley, R. C.↗
NASA NTRS1973

Early lunar history - Ages of 2 to 4 mm soil fragments from the lunar highlands

The ages of twenty-one 2 to 4 mm soil fragments from Apollo 16 stations 6, 8, 11, and 13, including all six major petrographic rock types found among Apollo 16 samples, were determined using the Ar-40/Ar-39 stepwise-heating technique. Twelve of the twenty-one samples have ages within 3.95 to 4.06 billion years, and it is believed that they represent the age of at least one stage of the Cayley Formation. Four samples have ages distinctly older than 4.00 billion years, making them the oldest lunar material found to date.

Schaeffer, O. A.↗
NASA NTRS1973

Cosmic-ray exposure history of North Ray and South Ray material

Cosmic-ray exposure ages for two breccias, 68815 and 69935, in the vicinity of South Ray Crater give consistent values of 2.0 plus or minus 0.2 m.y. when measured by the Kr-81-Kr, Na-22-Ne, and particle track methods. These also agree with estimates of exposure ages made by others using microcrater counts on six rocks in the same vicinity, including 69935. It is likely that this represents the age of South Ray Crater. Soils from stations close to South Ray Crater appear to be mature, well-irradiated materials containing little, if any, of a 2 m.y. component. Reviewing various lines of evidence, it is concluded that there are no compelling reasons to believe that so-called South Ray soils contain a large fraction of South Ray ejecta. However, if they do contain such ejecta, this material must have been well irradiated in situ prior to being thrown out in the South Ray event. A chip from a large boulder on the rim of North Ray Crater gives a Kr-81-Kr age of 50.6 plus or minus 3.8 m.y. Similar ages are found by the Na-22-Ne and the particle track methods. The agreement of this result with other data on large North Ray boulders fixes the age of North Ray Crater as 50 m.y.

Behrmann, C.↗
NASA NTRS1974

Surface history of lunar soil and soil columns

Measurements of cosmic ray track densities are presented for soil samples from Apollo 15, 16, and 17. Median track densities are used to infer total effective exposure times within about 15 cm of the lunar surface. Minimum track densities are used to derive the time of the last impact-produced rearrangement of soil grains. For samples from near various craters ages are derived of 40 m.y. for St. George, 6 (plus or minus 3) m.y. for S. Ray, 25 to 90 m.y. for Plum, and 20 to 35 m.y. for Shorty. The material of 15003, the Apollo 15 deep core at depths of 120 to 160 cm, is inferred to have been deposited at an average rate greather than or equal to 0.35 cm/m.y. The Apollo 16 core at 41 to 47 cm depths, 60007, appears to be well mixed and was covered up by deposition at greater than 0.3 cm/m.y. for the next few m.y. after its deposition.

Fleischer, R. L.↗
NASA NTRS1974

Studies of K-Ar dating and xenon from extinct radioactivities in breccia 14318; implications for early lunar history

The lunar breccia 14318 is one of three Apollo-14 breccias containing substantial amounts of parentless xenon from the spontaneous fission of extinct Pu-244. The argon and xenon contained in this breccia were studied by stepwise heating of pristine and neutron-irradiated samples. The isotopic composition of xenon from fission, determined by an improved method, is shown to be from Pu-244. Concentrations of this fissiogenic xenon are in substantial excess (15-fold) of what could be produced by spontaneous fission of U-238. The breccia is found to contain abundant trapped argon with an Ar-40/Ar-36 ratio of roughly 14. Otherwise, the argon is radiogenic and gives a convincing K-Ar age of 3.69 plus or minus 0.09 b.y. by the stepwise Ar-40/Ar-39 method, nearly in agreement with ages for other Apollo-14 breccias.

Reynolds, J. H.↗
NASA NTRS1974

Surface properties of the Orgueil meteorite - Implications for the early history of solar system volatiles

The Kr and H2O adsorption properties of Orgueil were studied. Dehydration by stepwise calcination produced a tenfold change in its B.E.T. surface area, which increased to 120 and then fell to 40 square meters per gram. Water exchangeability was measured by water regain from lab air between calcination cycles. Dehydration at room temperature showed that Orgueil contained 6 per cent by weight of water adsorbed on free surfaces. These results are consistent with an identification of Orgueil as montmorillonite, although chemical data conflict with this. High D/H ratios in CI carbonaceous chondrites may result from D enrichment in OH- groups during equilibration of dispersed phyllosilicate dust with preplanetary nebula gas at temperatures much less than 0 C.

Fanale, F. P.↗
NASA NTRS1974

On the irradiation history and origin of gas-rich meteorites

Transmission electron microscope study of the track density gradients and irradiation geometries of track-rich grains and chondrules in sections of Fayetteville and Kapoeta, and in sections of lunar breccias and grains from lunar soil. A substantial fraction (50 to 90%) of the meteoritic track-rich grains and chondrules show evidence of having been irradiated anisotropically in their different faces, as would be expected for irradiation on the surface of a parent body. The observations thus support the hypothesis that the irradiation of these grains and chondrules took place on the regoliths of asteroidal-sized bodies. Measurements of steepest track density gradients indicate that, while there are finite differences between spectra exhibited by individual gas-rich meteorites, the average solar flare spectral shapes have been similar over the last 4 b.y. or so.

Rajan, R. S.↗
NASA NTRS1974

Possible histories of the obliquity of Mercury

Possible evolutionary paths of the spin axis of Mercury are studied theoretically in terms of generalized Cassini's laws using the Hamiltonian approach. Three stable positions (Cassini states) of the spin axis are discerned. The Cassini states in which the spin axis remains fixed in the frame rotating with the orbit precession are extremes in the tide-free Hamiltonian under the condition of constant angular momentum. The stability of the 3/2 spin resonance for Mercury as a function of obliquity is discussed, and it is shown how control of the resonance is passed from one to another term in the averaged potential as the obliquity is increased with a corresponding loss of stability at each transfer. A sampling technique is used to infer the evolution due to tidal interaction. Two tidal models are used - one with a constant value of the specific dissipation function Q and the other with Q inversely proportional to frequency. An approximate analytic solution for precession trajectories very close to a Cassini state is developed.

Peale, S. J.↗
NASA NTRS1974

Evidence for an episode of crater obliteration intermediate in Martian history

It is shown that Mars experienced a brief episode of an increased obliteration rate contemporaneous with the formation of the cratered plains units. The obliteration rate during this episode was at least an order of magnitude greater than the preexisting rate. The obliteration rates prior to and after the event were identical within a factor of 3. Regional variations in the observed densities of degraded craters on the cratered terrain are shown to result from differences in the intensity of the obliteration rate during the event. The identification and characterization of the event are accomplished by using crater diameter-frequency distributions, not only for the total crater population but also for four morphological classes. Distributions are selected from 38 regions within the Martian equatorial latitudes.

Jones, K. L.↗
NASA NTRS1974

Clues in the rare gas isotopes to early solar system history

Rare gases in meteorites and lunar samples are discussed stimulating the discovery of the solar wind. Radioactive isotopes are examined, making a correlation to the origin of the solar system. It is shown that the heights of the peaks above the horizontal lines represent the spectrum of the fissiogenic sample. Nuclear tracks of iodine, xenon, and plutonium detected in lunar rocks are also explained.

Reynolds, J. H.↗
NASA NTRS1974

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 (0.69884 + or - 0.00004) 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 dos Reis and Allende are 4.62 x 10 to the 9th power years (4.62 billion years). 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 lower than the values estimated for the sources of KREEP (600-1000), high K (300-600) and low K (100-300) basalts.

Tatsumoto, M.↗