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  • LUNAR AND PLANETARY EXPLORATION  (15)
  • SPACE SCIENCES  (10)
  • 2010-2014
  • 1980-1984  (11)
  • 1975-1979  (3)
  • 1970-1974  (11)
  • 1960-1964
  • 1955-1959
  • 1950-1954
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Keywords
Years
Year
  • 1
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    Interstellar organic matter in meteorites (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Deuterium-enriched hydrogen is present in organic matter in such meteorites as noncarbonaceous chondrites. The majority of the unequilibrated primitive meteorites contain hydrogen whose D/H ratios are greater than 0.0003, requiring enrichment (relative to cosmic hydrogen) by isotope exchange reactions taking place below 150 K. The D/H values presented are the lower limits for the organic compounds derived from interstellar molecules, since all processes subsequent to their formation, including terrestrial contamination, decrease their D/H ratios. In contrast, the D/H ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites analyzed. The C-13/C-12 ratios of organic matter, irrespective of D/H ratio, lie well within those observed for the earth. Present findings suggest that other interstellar material, in addition to organic matter, is preserved and is present in high D/H ratio meteorites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 47; 2199-221
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  • 2
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    Saturn's rings - 3-mm observations and derived properties (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Three-millimeter Saturn observations, obtained from 1965 through 1977 and with Jupiter as a reference, have been used to derive a ring brightness temperature of 18 + or - 8 K. The brightness temperature of the disk of Saturn is 156 + or - 9 K. Part of the ring brightness (approximately 6 K) may be accounted for as disk emission which is scattered from the rings; the remainder (12 + or - 8K) is attributed to ring particle thermal emission. Because this thermal component brightness temperature is so much less than the particle physical temperature, limits are placed on the mean size and composition of the ring particles. In particular, as found by others, the particles cannot be rocky, but must be either metallic or composed of extremely low-loss dielectric material such as water ice. If the particles are pure water ice, for example, then a simple slab model and a multiple-scattering model both give upper limits to the particle sizes of approximately 1 m, a value three times smaller than previously available. The multiple-scattering model gives a particle single-scattering albedo at 3 mm of 0.83 + or - 0.13.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 41; Jan. 198
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  • 3
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    Millimeter-wave studies of the surfaces of Mercury and Mars and the atmosphere of Venus (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Disk average brightness temperatures of Mercury were obtained using a 4.6 m radio telescopes. The data was searched for periodicities which correlate with phase angle, hermocentric longitude and beat frequencies produced by modulations of various celestial mechanical parameters. Spectral line observations were made of Venus with the NRAO 11 m radio telescope. The total CO content and the CO vertical profile, and their variability were observed. Large scale thermophysical properties of the surface of Mars were studied.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-169867 , NAS 1.26:169867
    Format: application/pdf
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  • 4
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    Carbon, hydrogen and nitrogen isotopes in solvent-extractable organic matter from carbonaceous chondrites (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: CCl4 and CH3OH solvent extractions were performed on the Murray, Murchison, Orgueil and Renazzo carbonaceous chondrites. Delta-D values of +300-+500% are found in the case of the CH3OH-soluble organic matter. The combined C, H and N isotope data makes it unlikely that the CH3OH-soluble components are derivable from, or simply related to, the insoluble organic polymer found in the same meteorites. A relation between the event that formed hydrous minerals in CI1 and CM2 meteorites and the introduction of water- and methanol-soluble organic compounds is suggested. Organic matter soluble in CCl4 has no N, and delta-C-13 values are lower than for CH3OH-soluble phases. It is concluded that there either are large isotopic fractionations for carbon and hydrogen between different soluble organic phases, or the less polar components are partially of terrestrial origin.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 46; Jan. 198
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  • 5
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    The concentration and isotopic composition of hydrogen, carbon and nitrogen in carbonaceous meteorites (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Stepwise pyrolysis was used to extract H2, N2 and C from powdered meteorites and from meteorite residues resulting from partial dissolution in aqueous HF or from reaction with HF-HCl solutions. Concentrations and isotopic compositions were determined for the cases of the carbonaceous chondrites Orgueil, Murray, Murchison, Renazzo and Cold Bokkeveld. Acidification of the meteorites removed the organic sources of H2, so that H2 in the HF-HCl acid residues came mostly from the insoluble organic matter making up 70-80% of the total carbon in carbonaceous meteorites. Good correlation is found between delta-D and the concentration of H2 in the acid residues, but no correlation exists between the delta-D, delta-C-13 and delta-N-15 in them. A model is proposed for both the high delta-D values and the relationship between those values and the H2 concentration.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 46; Jan. 198
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  • 6
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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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  • 7
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    Synchrotron sources. II - Pulsars and compact extragalactic objects. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Discussion of some limitations on synchrotron models for optical pulsars and compact extragalactic objects. Using the results of a previous paper, it is shown that several existing models for the pulsar NP 0532 are inconsistent with the measured time variations and polarization of the optical emission. The possibility that the low-frequency falloffs in some extragalactic objects (PKS 2134 + 004, OQ 208, and NGC 1068) could be due to emission from particles with small pitch angles, absorption by a thermal plasma, or synchrotron self-absorption is also considered. It is found that radiation by particles with small pitch angles could explain the radio emission from PKS 2134 + 004 and OQ 208, but this process is inconsistent with the observations of NGC 1068. The absorption interpretations cannot account for the turnover in the spectrum of PKS 2134 + 004.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 183; July 15
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  • 8
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    Synchrotron sources. I - Extension of theory for small pitch angles. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Some of the features of synchrotron radiation are examined which occur when relativistic particles move at small pitch angles in a magnetic field. The emission from individual particles is computed. The general properties of the emission from distributions of particles with small pitch angles is discussed, and the emissivities and degrees of polarization for several specific source models are presented. For sources which mainly contain particles with small pitch angles, the degree of circular polarization will normally be high, whereas, if the magnetic field is somewhat irregular, the degree of linear polarization will be small. If the particle distribution also has a low-energy cutoff, the emissivity will vary linearly with frequency at low frequencies.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 183; July 15
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  • 9
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    Some aspects of cosmic synchrotron sources (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Synchrotron emission is considered from individual particles which have small pitch angles and the general properties of synchrotron sources which mainly contain such particles, as well as the emissivities and degrees of circular polarization for specific source distributions. The limitation of synchrotron source models for optical pulsars and compact extragalactic objects are discussed, and it is shown that several existing models for the pulsar NP 0532 are inconsistent with the measured time variations and polarizations of the optical emission. Discussion is made also of whether the low frequency falloffs in the extragalactic objects PKS 2134 + 004, OQ 208, and NGC 1068 is due to emission from particles with small pitch angles or absorption by a thermal plasma or synchrotron self-absorption. It is concluded that the absorption interpretations cannot account for the turnover in the spectrum of PKS 2134 + 004. Measurements of polarization, angular structure, and X-ray flux are also described.
    Keywords: SPACE SCIENCES
    Type: NASA-CR-131526 , SUIPR-435
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  • 10
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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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