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  • Other Sources  (8)
  • 2015-2019
  • 1985-1989  (8)
  • 1955-1959
  • 1985  (8)
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  • 2015-2019
  • 1985-1989  (8)
  • 1955-1959
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  • 1
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    The Evolution of CO2 on Mars (1985)
    In:  CASI
    Details
    Publication Date: 2014-10-08
    Description: The consequences of the hypothesis that the evolution of CO2 is directly linked to the occurrence of at least transitory pockets of moisture were exposed. The current conditions preclude the existence of open bodies of liquid water and the formation of moisture in disequilibrium is not excluded by any known constraints. The water evaporation rate is inversely proportional to PCO2, and the existence of a limiting value (P*) for which liquid water can form in the Mars environment is postulated. The evolution of PCO2 is controlled largely by relatively rapid aqueous chemistry forming carbon-containing sedimentary rocks, perhaps during early history in open water, but more recently in transitory pockets of moisture in the soil. Once the total atmospheric pressure is reduced to near P*, the occurrence of transitory moisture is inhibited, and atmospheric CO2 is no longer depleted by an efficient mechanism. The role of the carbonate reservoir in the current overall carbon budget on Mars, according to this scheme, is illustrated.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program; p 232-234
    Format: text
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  • 2
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    Error analyses for a gravity gradiometer mission (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper addresses the usefulness of an orbiting gravity gradiometer as a sensor for mapping the fine structure of the earth gravity field. The exact knowledge of this field is essential for studies of the solid earth and the dynamics of the oceans. Although the earth gravity tensor, measured by a gradiometer assembly, has nine components, only five components are independent. This latter fact is as a consequence of the symmetry and conservative nature of the earth's gravity field. The most dominant component is the radial one. The error analyses considered here are therefore based only upon a single axis gradiometer sensing this radial component. The expected global gravity and geoid errors for a 50 x 50-km (1/2 x 1/2 deg) area utilizing a spaceborne gradiometer with a precision of 0.001 EU in a 160-km circular polar orbit are about 3 mGAL and 5 cm, respectively.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-23; 527-530
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  • 3
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    Einstein observations of selected regions of the Cygnus Loop (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The imaging proportional counter on the Einstein X-ray Observatory is used to obtain high quality soft X-ray maps of two 40 x 40 arcmin regions of the Cygnus Loop. One region covers the western shock front; the other is centered on the southern diffuse extension. After careful correction for background and detector gain variations these two regions were subdivided for X-ray spectral analysis. In both cases the spectra of the brightest X-ray emitting areas are characterized by temperatures of about 2 million K, whereas the spectra of the fainter diffuse regions are indicative of higher temperatures (T greater than about 4 million K) and suggest the presence of a second, hard component. These results, together with the correlation of the X-ray spatial distribution with the optical and radio maps, are discussed in terms of current models of supernova remnant evolution. The evidence suggests that the Cygnus Loop is the result of a Type II supernova of a star of initial mass of less than about 20 solar masses.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 295; 456-462
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  • 4
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    The evolution of CO2 on Mars (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: At the surface, the atmosphere of Mars contains approximately 95.3 percent CO2 by volume. At the Viking Lander 1 (VL1) site, the total surface pressure varied with the season between about 6.89 and 8.94 mbar. Questions related to the observed CO2 pressure on Mars are explored. Several published estimates of the total amount of CO2 outgassed over the history of Mars, varying between 140 and 3000 mbar, are shown in a table. It is pointed out that the study of likely reservoirs for outgassed CO2 has focused mainly on the polar caps and regolith. Constraints on the formation of transitory pockets of moist soil are discussed, taking into account heat requirements, supply of water, and constraints related to pressure. Attention is also given to chemical considerations, implications for the current status of CO2 reservoirs, and scenarios for the evolution of CO2 pressure.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 62; 175-190
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  • 5
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    Space Science and Applications (1985)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The exploitation of the present tethered system and the need for repeat missions; multiple payloads placed along the tether; the extension of the present altitude limit to below 130 km; the development of free-flying tether satellites for studying both the Earth's atmosphere and ionosphere and also for studying the plantes; and a subtether were discussed. Areas of research were identified: aeronomy studies, gravity and magnetic potential mission, advanced sensors for geodynamics, and mapping and remote sensing.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: NASA. Marshall Space Flight Center Appl. of Tethers in Space, Vol. 2; 6 p
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  • 6
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    Participation in the Mars Data Analysis Program: Analysis of cloud forms in Viking and Mariner 9 images (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The first systematic account of the climate of Mars, based upon observations was produced. Cloud data were used to determine spatially and temporally varying near-surface wind direction, relative wind speed, static stability, and humidity conditions on a global scale. Existing models of meteorological processes were critically reexamined in light of the data, and more stringent constraints were set on global processes. Several discoveries were made, including the large extent and seasonal variability of the Mars equatorial Hadley cell, the failure of high latitude winds to reverse direction in early northern spring, the change in meridional wind component in southern midautum, and the almost constant cloud cover in the northern hemisphere, during spring and summer primarily by condensate clouds and in fall and winter by condensates and dust. The implications of these observations are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-175604 , NAS 1.26:175604
    Format: application/pdf
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  • 7
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    Einstein observations of the Vela supernova remnant - The spatial structure of the hot emitting gas (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Spatially resolved (aproximately 1 arcmin) X-ray maps of the Vela supernova remnant have been constructed in two spectral bands, 0.2-1.0 keV and 0.8-2.0 keV, from a series of 36 separate observations with the Imaging Proportional Counter of the Einstein Observatory. The maps exhibit substantial structure on all angular scales. Spectral analysis shows that the emission from the remnant can be consistently described as thermal radiation from hot gas which is nonuniform in density and temperature, but which is in approximate pressure equilibrium. It is found that p/k is approximately 3-4 x 10 to the 5th/cu cm K. The soft X-ray emission exhibits a high degree of correlation with the optical filamentary structure, in the sense that the most prominent filaments either tightly surround or are coincident with the brightest X-ray regions. This suggests that the softest X-radiation may originate in 'warm' gas which is evaporated from the denser clouds responsible for the optical and ultraviolet filaments. Such an interpretation is quantitatively investigated, and shown to be only marginally consistent with the observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 299; 821-827
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  • 8
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    Einstein observations of Vela X and the Vela pulsar (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The imaging detectors of the Einstein X-ray observatory have been used to study the Vela pulsar and its surrounding region. Although the pulsar is a relatively strong source of X-rays, there are not detectable pulsations at the pulsar period; the pulsed X-ray luminosity is less than approximately 10 to the 31st ergs/s in the 0.1-4.5 keV band. Nor is there evidence for other types of variability in the pulsar's X-ray emission. The images reveal structure on four spatial scales: (1) a pointlike object coincident with the pulsar; (2) a relatively bright, approximately 4-arcmin nebula of diffuse emission about the pulsar; (3) an approximately 1-degree nebula of hard emission that lies between the pulsar and the radio feature Vela X; and (4) thermal emission from the entire approximately 5-degree Vela supernova remnant. Spectral data from the small nebula are well fitted by a synchrotron model. Under the assumption that emission from the pulsar itself is thermal blackbody radiation, the surface temperature of the neutron star is calculated to be 1 million K.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 299; 828-838
    Format: text
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