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  • LUNAR AND PLANETARY EXPLORATION  (8)
  • 1985-1989  (8)
  • 1930-1934
  • 1
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    Identification of the youngest meteorites and a discussion of the possibility that they came from Mars (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The shergottites are a group of basaltic meteorites which are very similar in appearance to terrestrial basalts. On the Earth basalts are formed by volcanic activity. Because the shergottites so resemble terrestrial basalts and because they are apparently very young ( 1.3 billion years), it has been inferred that they come from a large planet. Small planets and asteroids lose heat from their interiors quickly and stop producing hot basaltic liquids early in their history. It appears that gases trapped in one shergotite found in Antarctica (BETA 79001) are chemically similar to the martian atmosphere (as measured by the Viking mission). The controversial speculation that the shergotites are samples of mars is examined in detail.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst. 16th Lunar and Planetary Sci. Conf.; p 38-41
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  • 2
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    A model for core formation in the early Earth (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two basic types exogenous models were proposed to account for siderophile and chalcophile element abundances in the Earth's upper mantle. The first model requires that the Earth be depleted in volatiles and that, after a core formation event which extracted the most siderophile elements into the core, additional noble siderophile elements (Pt, Ir, Au) were added as a late veneer and mixed into the mantle. The second model postulates a reduced Earth with approximately CI elemental abundances in which a primary core forming event depleted all siderophile elements in the mantle. The plausibility of models which require fine scale mixing of chondritic material into the upper mantle is analyzed. Mixing in liquids is more efficient, but large degrees of silicate partial melting will facilitate the separation of magma from residual solids. Any external events affecting the upper mantle of the Earth should also be evident in the Moon; but siderophile and chalcophile element abundance patterns inferred for the mantles of the Earth and Moon differ. There appear to be significant physical difficulties associated with chondritic veneer models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst. Workshop on the Early Earth: The Interval from Accretion to the Older Archean; p 42-44
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  • 3
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    Intelligent information extraction from reflectance spectra Absorption band positions (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A multiple high-order derivative analysis algorithm has been developed which can automatically extract absorption band positions from low-quality reflectance spectra with little degredation of accuracy. Overlapping bands with comparable widths and intensities can be resolved whose centers are as close as 0.3-0.5 W, with safer resolution limits of 0.6-1.0 W band center separations suggested for overlapping bands that are dissimilar. The segment length for smoothing is continually adjusted to about 0.5 W to minimize signal distortion, and a spectral pattern recognition algorithm predicts the signal spectrum and calculates approximate W across the spectrum using its second derivative. A single-pass cubic spline is applied to the smoothed data, and a sliding segment sixth-order polynomial is fit to the spectrum, with the length of the segment being continuously locally adjusted to 1.0 W across the spectrum. Good reliability and consistency of the algorithm is demonstrated with application to laboratory and earth-based telescope spectra.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 9585-959
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  • 4
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    Experimental investigations of trace element fractionation in iron meteorites. III - Elemental partitioning in the system Fe-Ni-S-P (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Measurements of solid metal/liquid metal trace element partition coefficients, which are used to interpret the crystallization history of magmatic iron meteorite groups differ greatly between different research groups, using different experimental techniques. Specifically, partition coefficients measured utilizing 'static' experiments which approach equilibrium cannot be reconciled with the results of 'dynamic' experiments which mimic fractional crystallization. We report new tests of our 'static' experimental technique and demonstrate that our methodology yields reliable equilibrium values for Ni, P and Ge partition coefficients. Partition coefficients in the Fe-Ni-S-P system are well matched by interpolation between the Fe-Ni-S and Fe-Ni-P subsystems. In contrast, the predictions of 'dynamic' experiments do not agree with our measurements and, consequently, the ability of 'dynamic' experiments to reproduce iron meteorite Ge vs. Ni fractionation trends successfully must be regarded as fortuitous.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 50; 1221-123
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  • 5
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    Geophysical constraints on lunar bulk composition and structure - A reassessment (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Theoretical lunar mantle seismic velocity and density profiles were calculated for a series of specific bulk composition models, thermal models, and evolutionary models. It was found that most of the calculated seismic profiles are in qualitative agreement with the Nakamura (1983) observational mantle seismic velocity model. With respect to the density modeling results, the most interesting finding is that none of the considered models yield mantle density increases that are sufficient to match the adapted upper bound on the lunar moment-of-inertia factor (0.3928). The results suggest that the moon possesses a dense metallic core with a mass in the range of 1 to 4 percent of the lunar mass and that the alumina-rich models of Morgan et al. (1978) and Taylor (1982) are best able to match the middle mantle velocity increase that characterizes the Nakamura model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; E396-E41
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  • 6
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    A discussion of isotopic systematics and mineral zoning in the shergottites - Evidence for a 180 m.y. igneous crystallization age (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The chronologies of the Shergotty, Zagami, ALHA 77005, and EETA 79001 meteorites were reexamined on the basis of shergottites' petrography and mineral chemistry data. Among the various isochrons, the concordant Rb-Sr (about 180 Myr) and U-Th-Pb (about 190 Myr) internal isochrons are interpreted as representing the time of igneous crystallization, while the Rb-Sr, Sm-Nd, and Pb-Pb whole-rock isochrons are interpreted as mixing lines, and are reasonably attributed to igneous processes such as wall-rock assimilation and magma mixing. If the approximated age of less than 200 Myr is correct, the shergottites represent the youngest known extraterrestrial basalts. This conclusion supports the hypothesis that the SNC meteorites are samples of Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 50; 969-977
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  • 7
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    Isotopic relationships among the shergottites, the nakhlites and Chassigny (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A model-based argument is made that there is a plausible relationship between the shergottites and the other SNCs which implies that the former contain an igneous component that is both young and mantle-derived. Evidence is presented that the shergottites were derived from a common mantle source within a short time interval and then interacted with other isotopic reservoirs prior to their crystallization. The model implies in general that the initial isotopic signatures of the bulk shergottites may be approximated as a mixing among three described components.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 14, 1988 - Mar 18, 1988; Houston, TX; United States
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  • 8
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    Origin of the earth's moon - Constraints from alkali volatile trace elements (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Although the moon is depleted in volatile elements compared to the earth, these depletions are not in accord with simple volatility. For example, the Cs/Rb ratios of the earth and moon inferred from basalt are approximately one seventh and one half of the CI ratio, respectively. Volatility considerations alone predict that the lunar Cs/Rb ratio should be equal to or lower than the terrestrial ratio if the moon was derived entirely from earth mantle material. Thus hypotheses such as rotational fission which invoke derivation of lunar material entirely from the earth's mantle may be excluded. The collisional ejection hypothesis of lunar origin requires at least 18 percent of lunar material to be derived from a projectile with dehydrated CI composition to match the lunar Cs/Rb ratio, and 25-50 percent to match both the lunar Cs/Rb ratio and absolute concentrations of Cs and Rb. It remains to be demonstrated that this relatively large contribution of projectile material is consistent with other elemental abundances and element ratios in the moon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 50; 91-98
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