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  • LUNAR AND PLANETARY EXPLORATION  (11)
  • AEROSPACE MEDICINE  (3)
  • ASTRONOMY  (2)
  • 2000-2004
  • 1980-1984  (16)
  • 1940-1944
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  • 11
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    Relic interstellar grains in Murchison meteorite (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is shown that, in the Murchison meteorite, the D/H ratios of hydrogen are unusually high in several separates and in one case up to 30 times the cosmic value of 2 x 10 to the -5th. Many phases show high C-13/C-12 ratios, up to 2.5 times the terrestrial value of 0.011. These C-13-rich and D-rich components of the two chemical elements are not correlated. They are heterogeneously distributed, suggesting that different components in the meteorite originated from different astrophysical sites and at different times. The D-rich hydrogen in the meteorite is probably due to molecules formed by ion-molecule reactions in interstellar clouds while the tiny amount of C-13-rich carbon is probably due to nucleosynthesis in red giant stars as suggested by Swart et al. (1983). Both of these heavy-isotope enriched components survived homogenization in the accumulation and subsequent history of the meteorites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 311; 544-547
    Format: text
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    NASA TECHNICAL REPORTS
  • 12
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    Mars - Subsurface properties from observed longitudinal variation of the 3.5-mm brightness temperature (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Extensive 3.5-mm measurements are reported which show a variation in the brightness temperature of Mars, with the Central Meridian Longitude that is generally in phase with the variation at 2.8 cm and is opposite in sign from the variations at 20 microns. It is pointed out that the phase result is not unexpected, since 3.5 mm is longer than the wavelength at which the phase behavior is expected to change. The result that the 3.5-mm rotation curve amplitude is larger than the amplitudes at both 20 microns and 2.8 cm, however, is unexpected. This result, it is noted, can be explained as a consequence of subsurface scattering from rocks smaller than 1.5 cm in radius. A correlation of subsurface scatterers with the location of the high-thermal inertial regions would be consistent with the hypothesis that rock abundance predominates in determining the thermal inertia.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 56; 465-475
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    NASA TECHNICAL REPORTS
  • 13
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    Saturn's rings - 3-mm low-inclination observations and derived properties (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: To determine a more precise brightness temperature and more accurate properties for Saturn's rings, 3.3 mm low inclination observations have been made at 90 GHz with the Aerospace 4.6 m radio telescope. A mean brightness temperature of 17 plus or minus 4 K has been determined by comparing the data with the variation of the inclination of the total flux from the planet and rings predicted by a simple model with uniformly bright A and B rings. Variation of the normal optical depth from 0.4 to 1.0 resulted in a total variation of about 1.5 K in A and B brightness. A portion of the brightness attributed to ring particle thermal emission has been determined to be at a temperature of 11 plus or minus 5 K. If the maximum particle radius (approximately 5 m) deduced from Voyager bistatic radar observations is correct, results indicate a particle distribution ranging between 1 cm and several meters radius of the form r exp -s with s = 3.3-3.6, or a material absorption coefficient ranging between 3 and 10 times lower than that of pure water ice at 85 K, or both. An increase in the porosity of the ice particles through a decrease in their density will not produce the observed particle albedo. If the rocky material is uniformly distributed, low ring brightness temperature would allow a silicate upper limit of approximately 10 percent by mass; however, the silicate material could be more abundant if it is separated from the icy material.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 58; 403-411
    Format: text
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    NASA TECHNICAL REPORTS
  • 14
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    Shock-induced devolatilization of calcite (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for calcite and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on calcite. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked calcite and their carbon and oxygen isotopic compositions were determined, and the shock-induced effect on the Mn(2+) electron spin resonance spectrum in the shock-recovered calcite was observed. On the basis of the obtained results, it is concluded that shock stresses at the 17-18 GPa level give rise to volatilization of 0.03-0.3 (mole) percent of calcite to CO2 and CO. The devolatilization of calcite occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters; 61; 1; Nov. 198
    Format: text
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  • 15
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    Silicon and oxygen isotopes in selected Allende inclusions (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Silicon and oxygen data are presented for a number of Allende samples. It is found that based on oxygen and silicon isotopes, Allende samples EGG-1, EGG-6, BG1a, and 3529Yc are typical, unfractionated Allende inclusions. Where magnesium data are available, they indicate the same thing. EGG-3 is fractionated in both oxygen and silicon, as it is in magnesium. Sample D7 melilite is fractionated in oxygen by several per mil along the C2-matrix line, away from typical Allende melilites. Inclusion BG10a is a FUN inclusion with an inferred original oxygen isotopic fractionation of 8-9 per mille/amu relative to the Allende line. Silicon data for two density fractions of inclusion 3A with different mineralogies show a difference of about 2 per mille, which indicates that silicon, like oxygen, has been added to at least some mineral phases in Allende inclusions from a reservoir other than the one in which the inclusion first began to form.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 16, 1981 - Mar 20, 1981; Houston, TX
    Format: text
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    NASA TECHNICAL REPORTS
  • 16
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    Carbon isotopic ratios in some low-delta N-15 lunar breccias (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Lunar soil breccias 10018, 79035 and 79135 were analyzed for carbon and nitrogen contents and isotopic compositions by vacuum pyrolysis, with a 500 C pre-combustion step in some cases. The combustion was used to remove carbon of terrestrial origin. Nitrogen isotopic ratios for the breccias are very low and are in agreement with results in the literature. Nitrogen yields in two cases were lower than literature values, a result attributable to heterogeneous mixing of implanted and implantation-free components in the breccias. Carbon isotopic ratios were found to be low in these breccias, even when reasonable account is taken of terrestrial carbon contamination. The results are consistent with the idea that low-delta N-15 values in lunar soils and breccias are accompanied by low-delta C-13 values, and imply that any secular variation which occurred in the delta N-15 of nitrogen implanted in lunar soils was accompanied by a similar but smaller variation in the delta C-13 of implanted carbon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 16, 1981 - Mar 20, 1981; Houston, TX
    Format: text
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