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  • 11
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    The Antarctic achondrite ALHA 76005 - A polymict eucrite (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: ALHA 76005 is a basaltic achondrite containing few, if any, orthopyroxenes. Its bulk major and trace element composition is like that of a non-cumulate eucrite, and unlike that of a howardite. It contains a variety of igneous clasts which differ in their textures, pyroxene/plagioclase ratios and pyroxene and plagioclase compositions. One clast, No. 4, was found to have the REE pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite. Both the chemical and oxygen isotopic composition of clast No. 4 suggest that it was derived from a source different from its host. These observations lead to the conclusion that ALHA 76005 is a polymict eucrite.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 45; Aug. 198
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  • 12
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    Oxygen isotopic compositions of chondrules in Allende and ordinary chondrites (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The ferromagnesian chondrules in Allende follow a trend in the oxygen three-isotope plot that diverges significantly from the 16-O mixing line defined by light and dark inclusions and the matrix of the meteorite. The trend probably results from isotopic exchange with an external gaseous reservoir during the process of chondrule formation sometime after the establishment of the isotopic compositions of the inclusions and matrix. The Allende chondrules approach, but do not reach, the isotopic compositions of chondrules in unequilibrated ordinary chondrites, implying exchange with a similar ambient gas, but isotopically different solid precursors for the two types of meteorite.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 13
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    Distribution and significance of chromium in meteorites (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Chromium is present as a minor element in all meteorite types. Depending on the meteorite type it is lithophile (most frequent), chalcophile (less frequent), or siderophile (rare). Chromium is an indicator of physical and chemical conditions of meteorite formation, especially of the state of oxidation. The Cr contents of meteoritic chromites are related to classification and can be used to distinguish among meteorite types that contain this mineral. The distribution of Cr between coexisting pyroxenes may indicate the degree of equilibration of this mineral pair. Siderophile Cr appears to result from primitive condensation processes rather than secondary reduction processes. The lack of much experimental data on Cr in silicate systems limits the interpretation of the occurrences of Cr-silicate phases, ureyite and krinovite, in the meteorite type in which they occur.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 14
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    Silicon in carbonaceous chondrite metal - Relic of high-temperature condensation (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Electron microprobe analyses of an extraordinarily large metal grain from the Murchison type 2 carbonaceous chondrite gave 0.24 mole % silicon. Thermodynamic calculations show that this is a natural consequence of condensation of alloys from the solar nebular gas at a total pressure between 10 to the -5th and 10 to the -3rd atm, provided they failed to equilibrate with it after cooling to less than 1200 K
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 206; Oct. 26
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  • 15
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    Venus. I - Carbon monoxide distribution and molecular-line searches (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An observational program to study variations of the vertical distribution of CO in the Venus atmosphere is presented. Measurements of the J = 0 - 1 absorption line at 2.6 mm wavelength are reported for two phase angles in 1977, one near eastern elongation (February) and the other near inferior conjunction (April). The two spectra are significantly different, with the April absorption line being narrower and deeper. The results of numerical inversion calculations show that the CO mixing ratio increases by a factor of approximately 100 between 78 and 100 km and that the CO abundance above approximately 100 km is greatest on the night-side hemisphere. These conclusions are in qualitative agreement with theoretical models. In addition to the CO observations, a search for other molecules was made to provide further information on the composition of the Venus middle atmosphere. The J = 0 - 1 transition of (C-13)O was detected and upper limits were derived for nine other molecules.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 45; Mar. 198
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  • 16
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    On the origin of isolated olivine grains in type 2 carbonaceous chondrites (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Two possibilities exist for the origin of aggregates and isolated grains in C2 meteorites: (1) high-temperature phases that condensed directly from a solar nebular gas accumulated as aggregates and single grains on the parent bodies of carbonaceous chondrites and remained unaltered since, or (2) all high-temperature phases in these meteorites are now, or once were, insided chondrules and have been melted out. Petrographic evidence for these two alternative models is examined critically. Four different scenarios to account for the kinds of aggregates and isolated grains in the Murchison C2 meteorite are studied. It is concluded that the majority of isolated olivine grains in the matrix never underwent melting in a chondrule-making stage. These crystal fragments and aggregates can thus be accounted for by direct condensation from a solar nebular gas.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters; 41; 2, Oc; Oct. 197
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  • 17
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    A scanning electron microscope study of olivine crystal surfaces (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: SEM photographs were taken of euhedral olivine grains from the Murchison C2 chondrite and several terrestrial and lunar occurrences. In general, the crystal faces of the meteorite grains are rough and uneven, with irregular growth patterns. They are very similar to crystal faces on terrestrial olivine grains that formed by sublimation from a vapor phase. They are very different from the relatively smooth and featureless surfaces of magmatic olivine crystals that precipitated from igneous melts. Qualitatively, the surface morphology of the crystal supports the contention that many euhedral crystals of olivine in C2 meteorites condensed from a gas phase.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics; 9; Sept. 30
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  • 18
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    Venus - Detection of variations in stratospheric carbon monoxide (1978)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The reported observations of the J = 0-1 rotational transition (115271.2 MHz) of carbon monoxide in the Venusian atmosphere indicate that the distribution of stratospheric CO is variable. Observations were obtained with a 11-m antenna on several days in February 1977, when Venus was near maximum eastern elongation (k approximately 0.4), and in April 1977 during inferior conjunction (k approximately 0.01). Differences in the line intensities and shapes for the two data sets are described. The results are interpreted to suggest that on the nightside of Venus there is relatively more CO at higher altitudes and relatively less CO at lower altitudes than on the dayside of the planet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Symposium on Planetary Atmospheres; Aug 16, 1977 - Aug 19, 1977; Ottawa; Canada
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  • 19
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    Cristobalite-pyroxene in an L6 chondrite - Implications for metamorphism (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: CRISPY is a cristobalite-pyroxene assemblage in the L6 chondrite ALHA 76003. It was formed by reaction of a very siliceous inclusion with the surrounding olivine-rich rock. Oxygen isotopes show that the inclusion was derived from a source with non-chondritic isotopic composition. The isotopes also show that the oxygen of the pyroxene reaction product was derived by simple mixing of oxygen from the inclusion and its immediately adjacent surroundings, with exchange with the bulk meteorite limited to a distance of about a millimeter. The persistence of cristobalite in close proximity to olivine, and the lack of isotopic equilibration, show that the metamorphic processes that form petrographic grade 6 chondrites involve transport of major elements over distances only on the order of millimeters.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters; 56; Dec. 198
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  • 20
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    Eleven new meteorites from Antarctica, 1976-1977 (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Basic petrographic, mineralogic, and chemical descriptions are given for all eleven meteorites recovered by the U.S.-Japan team in Antarctica during the austral summer 1976-1977. The meteorites are: Mt. Baldr a (H6), Mt. Baldr b (H6), Allan Hills 1 (L6), Allan Hills 2 (coarsest octahedrite, chemical group IA), Allan Hills 3 (L6), Allan Hills 4 (LL3), Allan Hills 5 (eucrite), Allan Hills 6 (H6), Allan Hills 7 (L6), Allan Hills 8 (H6), and Allan Hills 9 (L6).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics; 13; June 30
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