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  • 1
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    Mass spectrometric study of the mercury isotopes in the Allende meteorite (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Isotopic abundance ratios for mercury were determined by mass spectrometry in six samples of bulk material and in one sample of chondrules from the Allende meteorite. A primary purpose of the work was to attempt to verify the anomalous ratios reported for Hg-196/Hg-202 by neutron activation. Measurements were made on the mercury released at temperatures of 250, 450, 600 C, and in some cases, higher temperatures. The precision of the measurements was such that if an anomaly of the magnitude reported exists, it should have been seen. The isotopic abundance ratios for the other mercury isotopes were also measured. Within the errors of measurement these agreed with normal terrestrial values.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; E124-E12
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  • 2
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    Helium and neon isotopes in deep Pacific Ocean sediments (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Helium and neon concentration measurements, along with isotope ratio determinations, have been made for particles collected in the deep Pacific with a magnetic sled, and they are believed to be of extraterrestrial origin. Analyses were made for samples consisting of composites of many extremely fine particles and for several individual particles large enough to contain sufficient gas for analysis but small enough to escape melting in their passage through the atmosphere. Step-heating was employed to extract the gas. Cosmic-ray spallation products or solar-wind helium and neon, if present, were not abundant enough to account for the isotopic compositions measured. In the case of the samples of magnetic fines, the low temperature extractions provided elemental and isotopic ratios in the general range found for the primordial gas in carbonaceous chondrites and gas-rich meteorites. The isotopic ratios found in the high temperature extractions suggest the presence of solar-flare helium and neon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 173-182
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  • 3
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    Venus thermosphere - In situ composition measurements, the temperature profile, and the homopause altitude (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The neutral mass spectrometer on board the Pioneer Venus multiprobe bus measured composition and structural parameters of the dayside Venus upper atmosphere on 9 December 1978. Carbon dioxide and helium number densities were 6 x 10 to the 9th and 5 x 10 to the 6th per cubic centimeter, respectively, at an altitude of 150 kilometers. The mixing ratios of the both argon-36 and argon-40 were approximately 80 parts per million at an altitude of 135 kilometers. The exospheric temperature from 160 to 170 kilometers was 285 plus or minus 10 K. The helium homopause was found at an altitude of about 137 kilometers.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 203; Feb. 23
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  • 4
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    The search for organic substances and inorganic volatile compounds in the surface of Mars (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A total of four Martian samples, one surface and one subsurface sample at each of the two Viking landing sites, Chryse Planitia and Utopia Planitia, have been analyzed for organic compounds by a gas chromatograph-mass spectrometer. In none of these experiments could organic material of Martian origin be detected at detection limits generally of the order of parts per billion and for a few substances closer to parts per million. The evolution of water and carbon dioxide, but not of other inorganic gases, was observed upon heating the sample to temperatures of up to 500 C. The absence of organic compounds seems to preclude their production on the planet at rates that exceed the rate of their destruction. It also makes it unlikely that living systems that behave in a manner similar to terrestrial biota exist, at least at the two Viking landing sites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 82; Sept. 30
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  • 5
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    The upper atmosphere of Venus during morning conditions (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The structure and composition of the Venus upper atmosphere between 130- and 650-km altitude were measured for a solar zenith angle of approximately 60 deg by the neutral gas mass spectrometer on board the Pioneer Venus multiprobe bus. Below 180 km a wavelike structure is quite evident in the CO2 and He number density profiles. For altitudes above 100 km a one-dimensional model of the Venus upper atmosphere during morningside conditions (MS model) is presented. Number densities at 150-km altitude are as follows: CO2 equals 4.2 x 10 to the 9th, N2 equals 1.1 x 10 to the 9th, CO equals 2.8 x 10 to the 9th, and He equals 4.8 x 10 to the 6th per cu cm. The homopause altitudes for N2 and He are at 136 and 130 km, respectively.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 85; Dec. 30
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  • 6
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    Search for organic and volatile inorganic compounds in two surface samples from the Chryse Planitia region of Mars (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Two surface samples collected from the Chryse Planitia region of Mars were heated to temperatures up to 500 C, and the volatiles that they evolved were analyzed with a gas chromatograph-mass spectrometer. Only water and carbon dioxide were detected. This implies that organic compounds have not accumulated to the extent that individual components could be detected at levels of a few parts per billion by weight in the samples. Proposed mechanisms for the accumulation and destruction of organic compounds are discussed in the light of this limit.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 194; Oct. 1
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  • 7
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    Isotopic composition of nitrogen - Implications for the past history of Mars' atmosphere (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Models are presented for the past history of nitrogen on Mars, based on Viking measurements showing that the atmosphere is enriched in N-15. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2(+). The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 194; Oct. 1
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  • 8
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    Isotopic composition of the Martian atmosphere (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Results from the neutral mass spectrometer carried on the aeroshell of Viking 1 show evidence for NO in the upper atmosphere of Mars and indicate that the isotopic composition of carbon and oxygen is similar to that of earth. Mars is enriched in N-15 relative to earth by about 75 per cent, a consequence of escape that implies an initial abundance of nitrogen equivalent to a partial pressure of at least 2 millibars. The initial abundance of oxygen present either as CO2 or H2O must be equivalent to an exchangeable atmospheric pressure of at least 2 bars in order to inhibit escape-related enrichment of O-18.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 194; Oct. 1
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  • 9
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    Composition and structure of the Martian atmosphere - Preliminary results from Viking 1 (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Results from the aeroshell-mounted neutral mass spectrometer on Viking 1 indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180 plus or minus 20 deg K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241 deg K. The descent data are consistent with the view that CO2 should be the major constituent of the lower Martian atmosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 193; Aug. 27
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  • 10
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    The thermal history of interplanetary dust particles collected in the Earth's stratosphere (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Fragments of 24 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were obtained from NASA's Johnson Space Center collection and subjected to pulse-heating sequences to extract He and Ne and to learn about the thermal history of the particles. A motivation for the investigation was to see if the procedure would help distinguish between IDPs of asteroidal and cometary origin. The use of a sequence of short-duration heat pulses to perform the extractions is an improvement over the employment of a step-heating sequence, as was used in a previous investigation. The particles studied were fragments of larger parent IDPs, other fragments of which, in coordinated experiments, are undergoing studies of elemental and mineralogical composition in other laboratories. While the present investigation will provide useful temperature history data for the particles, the relatively large size of the parent IDPs (approximately 40 micrometers in diameter) resulted in high entry deceleration temperatures. This limited the usefulness of the study for distinguishing between particles of asteroidal and cometary origin.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 28; 5; p. 675-681
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