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  • 1
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    A model of impulsive acceleration and transport of energetic particles in Mercury's magnetosphere (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A qualitative model of substorm processes in the Mercury magnetosphere is presented based on Mariner 10 observations obtained in 1974-1975. The model is predicated on close analogies observed with the terrestrial case. Particular emphasis is given to energetic particle phenomena as observed by Mariner on March 29, 1974. The suggestion is supported that energetic particles up to about 500 keV are produced by strong induced electric fields at 3 to about 6 Mercury radii in the Hermean tail in association with substorm neutral line formation. The bursts of energetic particles produced are, in this model, subsequently confined on closed field lines near Mercury and drift adiabatically on quasi-trapped orbits for many tens of seconds. Such gradient and curvature drift of the particles can explain prominent periodicities of 5-10 s seen in the Mariner for greater than 170-keV electron flux profiles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 8742-874
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  • 2
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    Radio-interferometric imaging of the subsurface emissions from the planet Mercury (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The distribution of total and polarized intensities from Mercury's subsurface layers have been mapped using VLA observations. The first detection of a hot pole along the Hermean equator is reported and modeled as black-body reradiation from preferential diurnal heating. These observations appear to rule out any internal sources of heat within Mercury. Polarized emission from the limb of the planet is also found, and is understood in terms of the dielectric properties of the Hermean surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 329; 224-226
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  • 3
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    Fluvial valleys and Martian palaeoclimates (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Theoretical models of early Martian atmospheric evolution describe the maintenance of a dense CO2 atmosphere and a warm, wet climate until the end of the heavy-bombardment phase of impacting. However, the presence of very young, earthlike fluvial valleys on the northern flank of Alba Patera conflicts with this scenario. Whereas the widespread ancient Martian valleys generally have morphologies indicative of sapping erosion by the slow outflow of subsurface water, the local Alba valleys were probably formed by surface-runoff processes. Because subsurface water flow might be maintained by hydrothermal energy inputs and because surface-runoff valleys developed late in Martian history, it is not necessary to invoke drastically different planet-wide climatic conditions to explain valley development on Mars. The Alba fluvial valleys can be explained by hydrothermal activity or outflow-channel discharges that locally modified the atmosphere, including precipitation and local overland flow on low-permeability volcanic ash.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 341; 514-516
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  • 4
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    Paleohydrologic Implications of Valley Networks of Mars (1985)
    In:  CASI
    Details
    Publication Date: 2014-10-08
    Description: Valley networks in the heavily cratered terrains of Mars represent an ancient epoch of hydrologic conditions greatly different from those of today. Available crater counts on the valley networks indicate formation during the high flux of impacting bodies charaterizing the early heavy bombardment phase of Martian history. Two populations of valleys are recognized in the equatorial regions of Mars: pristine and degraded. The latter probably formed at the very end of the heavy bombardment phase, extending into the post-heavy bombardment by formation in the intercrater plains. Pristine valleys generally form segments of larger networks with degraded components. This suggests that valley formation was a prolonged process coeval with the heavy bombardment period and extending just beyond that period in martian history. The pristine networks and pristine portions of compound networks on Mars show morphological attributes consistent with an origin by headward growth through spring sapping. On Earth spring sapping occurs where groundwater out-streamflow can be generated by insolation changes associated with orbital parameters or with geothermal effects, such as might be associated with impact or with the volcanic emplacement of the intercrater plains. Thus, it is appropriate to specify the most conservation deviation from modern hydrologic conditions on Mars that could account for the ancient epoch of valley formation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program; p 313-315
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  • 5
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    Fluvial valleys on Martian volcanoes (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Channels and valleys were known on the Martian volcanoes since their discovery by the Mariner 9 mission. Their analysis has generally centered on interpretation of possible origins by fluvial, lava, or viscous flows. The possible fluvial dissection of Martian volcanoes has received scant attention in comparison to that afforded outflow, runoff, and fretted channels. Photointerpretative, mapping, and morphometric studies of three Martian volcanoes were initiated: Ceraunius Tholus, Hecate Tholus, and Alba Patera. Preliminary morphometric results indicate that, for these three volcanoes, valley junction angles increase with decreasing slope. Drainage densities are quite variable, apparently reflecting complex interactions in the landscape-forming factors described. Ages of the Martian volcanoes were recently reinterpreted. This refined dating provides a time sequence in which to evaluate the degradational forms. An anomaly has appeared from the initial study: fluvial valleys seem to be present on some Martian volcanoes, but not on others of the same age. Volcanic surfaces characterized only by high permeability lava flows may have persisted without fluvial dissection.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 294-296
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  • 6
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    The channels of Mars (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: AAS PAPER 86-156
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  • 7
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    The magnetosphere of Mercury (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Data provided by the Mariner-10 spacecraft on the properties of Mercurian magnetosphere are examined. These observations indicate that the Mercurian magnetosphere has a magnetopause and a bow shock which are quite similar to their terrestrial counterparts, although much smaller. However, due to the absence of any significant atmosphere or ionosphere, the flow of current in the Mercurian magnetosphere is different from the patterns at the earth. Many questions regarding the intrinsic magnetic field properties of Mercury remain unanswered, such as the existence of radiation belts, magnetic storms, the size of auroral regions, the mechanism of global magnetospheric convection, and the source of plasma.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 8
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    Energetic ions upstream of Jupiter's bow shock (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In an analysis of the Jovian ion events, Baker et al. (1984) have found that there appears to be a spectral hardening as the interplanetary magnetic field (IMF) changed orientation from the postnoon to a prenoon connection point. It was also observed that ion events were accompanied by long-period (approximately 10 min) waves whose presence was weakly related to a decrease in the ion anisotropy. The present investigation examines in substantial detail the development of the ion energy spectrum over the full range (approximately 30 keV to approximately 4 MeV). The results of the investigation show that the energy spectra are dominated by heavy ions (presumed to be oxygen and sulfur) at higher (approximately equal to or greater than 300 keV) energies.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 3947-396
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  • 9
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    Polar cap photoionization and the ten-hour clock at Jupiter (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is shown that the clock-like modulation of the spectral index of energetic electrons (greater than 2 MeV) in the outer Jovian magnetosphere is due to a periodic shift of the particle energy spectrum toward higher and lower energies. This shift results in a modulation of the spectral index when the spectrum is not a pure power law in energy. It is suggested that the periodic energization is due to a periodic modulation of the magnetic field in the outer magnetosphere. This modulation is caused by a variation of the longitudinally averaged Pedersen conductivity due to the asymmetric solar illumination of the trace of the magnetodisk in the high-latitude ionospheres. Such a modulation requires the presence of a surface magnetic anomaly.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 6304-631
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  • 10
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    MECA Symposium on Mars: Evolution of its Climate and Atmosphere (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The geological, atmospheric, and climatic history of Mars is explored in reviews and reports of recent observational and interpretive investigations. Topics addressed include evidence for a warm wet climate on early Mars, volatiles on Earth and on Mars, CO2 adsorption on palagonite and its implications for Martian regolith partitioning, and the effect of spatial resolution on interpretations of Martian subsurface volatiles. Consideration is given to high resolution observations of rampart craters, ring furrows in highland terrains, the interannual variability of the south polar cap, telescopic observations of the north polar cap and circumpolar clouds, and dynamical modeling of a planetary wave polar warming mechanism.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-182872 , NAS 1.26:182872 , LPI-TR-87-01 , Jul 17, 1986 - Jul 19, 1986; Washington, DC; United States
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