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At least 973 records · Page 54

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NASA NTRS1973

Atmophilic elements in lunar soils

Ten volatile elements are more abundant in soil 14163 than in 14259 by factors of 1.4 or greater, too high to be explained by the 15% higher KREEP content of 14163. The enrichments suggest that these elements are easily volatilized by energetic events generated by solar particles or micrometeorites and as a result move from site to site through the lunar atmosphere. The elements Zn, C, and Cd are correlated with excess Ar-40 in Apollo 15 soils. Since concentrations also increase in the direction of the Apennine Front, the correlation chiefly indicates that the Front regolith is enriched in these elements relative to the Apollo 15 regolith away from the Front. The absence of known lunar rock types showing Zn and Cd concentrations as high as those in the Apollo 15 Front regolith or the Apollo 14 or 16 highlands regoliths and the relatively uniform concentrations of both elements in these soils despite differences in major element composition suggest that large amounts of these elements were released as volatiles during early lunar magmatic activity.

Chou, C.-L.↗

NASA NTRS1973

Carbon and sulfur distributions and abundances in lunar fines

Total sulfur abundances have been determined for 20 Apollo 14, 15, and 16 soil samples and one Apollo 14 breccia. Sulfur concentrations range from 474 to 844 microg S/g. Volatilization experiments on selected samples have been carried out using step-wise heating. Sample residues have been analyzed for their total carbon and sulfur abundances to establish the material balance in lunar fines for these two elements. Volatilization experiments have established that between 31 to 54 microg C/g remains in soils which have been heated at 1100 C for 24 hours under vacuum. The residual carbon is believed to be indigenous lunar carbon whereas all forms of carbon lost from samples below 1100 C is extralunar carbon. Total carbon and sulfur abundances taken from the literature have been used to show the depletion of volatile elements with increasing grade for the Apollo 14 breccias.

Gibson, E. K., Jr.↗

NASA NTRS1974

Dielectric comparison of lunar and terrestrial fines at lunar conditions

The dielectric properties of lunar fines 74241,2 in the audio-frequency range under lunarlike conditions are presented. Results suggest that volatiles are released during storage and transport of the lunar sample. Apparently, subsequent adsorption of volatiles on the sample surface alters its dielectric response. The assumed volatile influence disappears after evacuation. A comparison of the dielectric properties of lunar and terrestrial materials as a function of density, temperature, and frequency indicates that if the terrestrial sample analyzed were completely devoid of atmospheric moisture, it would present dielectric losses smaller than those of the lunar sample. It is concluded that density prevails over temperature as the controlling factor of dielectric permittivity in the lunar regolith and that dielectric losses vary slowly with depth.

Alvarez, R.↗

NASA NTRS1976

The making of the atmosphere

A model for the evolution of the earth's atmosphere is proposed in which the atmosphere and oceans are assumed to have accumulated as a result of volatile outgassing from the earth's interior. The bulk of the outgassed volatiles were originally trapped within the solid earth during the planetary accretion process, while other volatiles resulted from radiogenic decay within the solid earth. Atmospheric oxygen resulted from the photo-dissociation of water vapor during the earth's early history and from photosynthetic activity in more recent times. The origin and evolution of atmospheric ozone is closely related to the growth of oxygen. The rise of ozone and the evolution of life is discussed in terms of an evolving oxygen atmosphere.

Levine, J. S.↗

NASA NTRS1977

Lithic clasts in the Supuhee chondrite

Bulk chemical analyses of three foreign lithic clasts from Supuhee, a shocked and brecciated H6 chondrite, were carried out in an attempt to locate 'mysterite', a volatile-rich material postulated to be present. Clast 1 bears some similarities to C1 and C2 chondrites, but its relatively low (less than 9.4%) volatile content suggests a different set of physicochemical conditions during low-temperature condensation. Clast 2 was apparently derived from H-group chondrite material by loss of metal and sulfide. Clast 3 is an unusual meteorite type whose chemical composition is reminiscent of the unique chondrite Kakangari (Graham, et al., 1977). These chemically distinct bodies were apparently not present during the metamorphic event which affected Supuhee. Although the presence of mysterite was not confirmed or refuted, the present results indicate that conditions were favorable for the formation, incorporation and preservation of volatile-rich materials.

Leitch, C. A.↗

NASA NTRS1977

'Mysterite' - A late condensate from the solar nebula

An attempt is made to clarify the nature of 'mysterite', a material that had been postulated to explain the overabundance of Tl, Bi, and Ag in certain chondrites. Four dark clasts and a vein sample from the H6 chondrite Supuhee were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Rb, Re, Sb, Se, Te, Tl, and Zn. One of the clasts is enriched in all volatile elements, while the other four samples are enriched only in the siderophile volatiles Ag, Bi, and Tl. The enrichments range up to 100 times typical H6 chondrite abundances. The proportions of Ag, Bi, and Tl suggest the presence of at least two, Tl-rich and Tl-poor, varieties of mysterite. The former seems to dominate in Supuhee and Krymka, and the latter in Mezo-Madaras. Apparently mysterite is a late condensate from the solar nebula that collected volatiles left behind by earlier generations of chondrites. It was incorporated in Supuhee and perhaps in other chondrites (mainly of low petrologic types) during brecciation events.

Higuchi, H.↗

NASA NTRS1977

Internal friction quality-factor Q under confining pressure

It has been found in previous studies that small amounts of adsorbed volatiles can have a profound effect on the internal friction quality-factor Q of rocks and other porous media. Pandit and Tozer (1970) have suggested that the laboratory-measured Q of volatile-free rocks should be similar to the in situ seismic Q values of near-surface lunar rocks which according to Latham et al. (1970) are in the range of 3000-5000. Observations of dramatic increases in Q with outgassing up to values approaching 2000 in the seismic frequency range confirm this supposition. Measurements under confining pressures with the sample encapsulated under hard vacuum are reported to aid in the interpretation of seismic data obtained below the lunar surface. It has been possible to achieve in the experiments Q values just under 2000 at about 1 kbar for a terrestrial analog of lunar basalt. It was found that a well-outgassed sample maintains a high Q whereas one exposed to moisture maintains a low Q as the confining pressure is raised to 2.5 kbar. This result suggests that volatiles can indeed affect Q when cracks are partially closed and the high lunar seismic Q values reported are concomitant with very dry rock down to depths of at least 50 km.

Tittmann, B. R.↗

NASA NTRS1978

Fractionation in the solar nebula. II - Condensation of Th, U, Pu and Cm

Reasonable assumptions concerning activity coefficients allow the calculation of the relative volatility of the actinide elements under conditions expected during the early history of the solar system. Several of the light rare earths have volatilities similar to Pu and Cm and can be used as indicators of the degree of fractionation of these extinct elements. Uranium is considerably more volatile than either Pu or Cm, leading to fractionations of about a factor of 50 and 90 in the Pu/U and Cm/U ratio in the earliest condensates from the solar nebula. Ca,Al-rich inclusions from the Allende meteorite, including the coarse-grained inclusions, have a depletion of U relative to La of about a factor of three, suggesting that these inclusions may have been isolated from the nebular gas before condensation of U was complete. The inclusions, however, can be used to determine solar Pu/U and Cm/U ratios if the rare earth patterns are determined in addition to the other normal measurements.

Boynton, W. V.↗

NASA NTRS1978

Continuous extrusion of coal

A feeding method for use with bituminous coals that exhibit plasticity at elevated temperatures is described and demonstrated on a small screw extruder previously used to extrude polyethylene. A metered feed of coal heated to a temperature just below that of incipient caking (approximately 450 C) is used. Modifications to the extruder consisting of ceramic band heaters, auxiliary cooling coils on the thrust bearing and special quick opening dies are detailed. Coals successfully extruded include high volatile A bituminous coals, high volatile B bituminous coals, a high volatile C bituminous coal and a coal with high ash content. The computer program, EXTRUD, used to simulate the extruder is described. Predicted power consumption exhibits 30% scatter, which is explained by the sensitivity of the coal friction coefficient to temperature profiles. Detailed analysis reveals some discrepancies in the program that need to be resolved.

England, C.↗

NASA NTRS1979

Dust release and mantle development in comets

A model of dust release and dust mantle development by cometary nuclei is developed to explain the brightness asymmetry observed in comets before and after perihelion. Assuming that the cometary nucleus consists of a uniform mixture of dust and volatile ices and taking into account the differential mass spectrum of the dust and the effect of nuclear gravity, it is shown that the factor which determines whether a comet will be brighter before or after perihelion is the mass ratio of dust to volatiles in the nucleus. If this ratio is greater than about two, the comet will be brighter on the inward path and not lose its mantle near perihelion. Applying the model to comet Halley (dust to volatiles ratio presumed to be less than two), it is predicted that the comet remains without a mantle until it reaches a heliocentric distance of 2.035 AU after perihelion and loses its mantle suddenly at a distance of about 1.45 AU on the inward path, causing it to be brighter after perihelion. Predictions of monochromatic brightness are found to be in fair agreement with total observed brightnesses.

Brin, G. D.↗

NASA NTRS1979

Implications of the gas compositional measurements of Pioneer Venus for the origin of planetary atmospheres

Comparisons are made between the volatile inventories of the terrestrial planets, including Pioneer Venus data, and the predictions of three classes of theories for the origin of planetary atmospheres. Serious difficulties arise for the primary atmosphere and external source hypotheses. The grain accretion hypothesis can account for the trends in the volatile inventory from Venus to earth to Mars, if volatiles were incorporated into planet-forming grains at nearly the same temperature for all of these planets, but at systematically lower pressures in the regions of planet formation farther from the center of the solar nebula.

Pollack, J. B.↗

NASA NTRS1979

Sulfur volcanoes on Io

Widespread volcanism on Jupiter's satellite Io, if it occurred over the age of the solar system, would quickly reduce the inventory of most common volatiles needed to drive such volcanism. One exception is the volatile element sulfur. It is therefore postulated that sulfur is the driving volatile for Ionian volcanism. Its presence is consistent with a carbonaceous-chondrite-like bulk composition for the original material that formed Io 4.5 billion years ago. The ubiquity of sulfur on Io today demonstrates the importance of this element in the processes that formed its surface.

Consolmagno, G. J.↗

NASA NTRS1979

Isotopic anomalies of noble gases in meteorites and their origins. III - LL-chondrites

Nine LL-chondrites were studied by selective etching to characterize the noble gas components in three mineral fractions: HF-HCl-solubles, chromite and carbon. The Ne-20/Ar-36 ratio is considered, noting that chondrites of different petrologic types cannot all be derived from the same volatile rich ancestor, but must have formed over a range of temperatures, with correspondingly different volatile contents. Variations in the carbonaceous chondrite fission (CCFXe) component in LL3, LL5, and LL6 chondrites are discussed, noting that if CCFXe comes from a supernova, then its distribution in LL-chondrites requires three presolar carrier minerals of the right solubility properties, containing three different xenon components. However, if CCFXe comes from fission of a volatile superheavy element, then its decrease from LL3 to LL6 can be attributed to less complete condensation from the solar nebula. Finally, the three types of primordial xenon components which occur in different minerals of the same meteorite are described.

Alaerts, L.↗

NASA NTRS1979

Isotopic anomalies of noble gases in meteorites and their origins. IV - C3 /Ornans/ carbonaceous chondrites

The C3O chondrites Kainsaz, Lance, and Ornans were studied by an acid dissolution technique to characterize the noble gas components in 3 mineral fractions: HF, HCl-solubles, chromite and carbon, and 'phase Q', a trace mineral containing Ar, Kr, Xe. For all fractions, gas contents decline in the order Kainsaz, Lance, Ornans; this trend parallels volatile contents but not heterogeneity of olivine composition or degree of metamorphism, and reflects progressively higher condensation temperature from the solar nebula. The Ar/Xe ratios and compositions of the three mineral fractions are discussed, and it is concluded that in all primitive chondrites the amount and the chemical separability of CCFXe parallel the abundance of primordial noble gases and other volatiles, such as C, N, Tl, Bi, and In. The close correlation of CCFXe with properties of local origin, such as volatile content and petrologic type, is more consistent with a local than with an extrasolar origin of the component.

Alaerts, L.↗

NASA NTRS1979

74001 drive tube - Siderophile elements match II B iron meteorite pattern

Eight siderophile elements, seven volatile elements, and U were determined in three samples from 74001 by radiochemical neutron activation analysis. The siderophile pattern closely corresponds to the addition of approximately 0.1% of II B iron meteorites, and the enrichment of nonsiderophile volatile elements seems to be derived from lunar sources with variation generally following Se content. In addition, in 74001 (predominantly black glass), moderately volatile elements (Ag, Zn) are more abundant than In, Cd, and particularly Bi, while in 74220 (mainly orange glass), Ag, Zn, In, and Cd are almost equally abundant, but Bi is as low as in 74001.

Morgan, J. W.↗

NASA NTRS1980

Chemical fractionations in meteorites. XI - C2 chondrites

Measurements of the compositions of 20 trace elements in the representative C2 chondrites Boriskino, Cold Bokkeveld, Erakot, Essebi, Haripura, Santa Cruz and Al Rais are reported. The contents of Ag, Au, Bi, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Sn, Te, Tl, U, and Zn were determined by radiochemical neutron activation analysis. The siderophile abundances of the C2 chondrites are found to be less uniform than those of other carbonaceous chondrites, while the C2R chondrite Al Rais is systematically lower in 12 volatiles than the C2M chondrites. Enrichment of Bi and Tl found in Erakot and Haripura indicate the possible presence of the late condensate mysterite. Volatile abundances are shown to agree with matrix contents for meteorites that have suffered little aqueous alteration, however to be 20-30% lower for the more altered meteorites. Finally, the decline of element abundance with volatility is shown to be consistent with the sigmoid curve explained by the two-component model.

Wolf, R.↗

NASA NTRS1982

IUS materials outgassing condensation effects on sensitive spacecraft surfaces

Four materials used on the inertial upper state (IUS) were subjected to vacuum conditions and heated to near-operational temperatures (93 to 316 C), releasing volatile materials. A fraction of the volatile materials were collected on 25 C solar cells, optical solar reflectors (OSR's) or aluminized Mylar. The contaminated surfaces were exposed to 26 equivalent sun hours of simulated solar ultraviolet (UV) radiation. Measurements of contamination deposit mass, structure, reflectance and effects on solar cell power output were made before and after UV irradiation. Standard total mass loss - volatile condensible materials (TML - VCM) tests were also performed. A 2500 A thick contaminant layer produced by EPDM rubber motor-case insulation outgassing increased the solar absorptance of the OSR's from 0.07 to 0.14, and to 0.18 after UV exposure. An 83,000 A layer caused an increase from 0.07 to 0.21, and then the 0.46 after UV exposure. The Kevlar-epoxy motor-case material outgassing condensation raised the absorptance from 0.07 to 0.13, but UV had no effect. Outgassing from multilayer insulation and carbon-carbon nozzle materials did not affect the solar absorptance of the OSR's.

Mullen, C. R.↗

NASA NTRS1981

Thermal modeling of cometary nuclei

A model of the sublimation of volatile ices from a cometary nucleus is presented which includes the effects of (1) diurnal heating and cooling, (2) rotation period and pole orientation, (3) the thermal properties of the ice and subsurface layers, and (4) the contributions from coma opacity, scattering and thermal emission where the properties of the coma are derived from the integrated rate of volatile production by the nucleus. In applying the model to the case of the 1986 apparition of Halley's comet, it is found that the generation of a cometary dust coma increases the total energy reaching the Halley nucleus due to the greater geometrical cross-section of the coma as compared with the bare nucleus. The calculated coma opacity of Halley is about 0.2 at 1 AU from the sun and 1.2 at perihelion. Possible consequences of the results obtained for the generation of nongravitational forces, volatile production rates for comets and cometary lifetimes against sublimation are discussed.

Weissman, P. R.↗