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  • LUNAR AND PLANETARY EXPLORATION  (1,501)
  • 1
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    Superthermal ions detected in Venus' dayside ionosheath, ionopause, and magnetic barrier regions (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results of a comprehensive morphological analysis of the dayside superthermal ion presence in the dayside ionopause region of Venus made using the Orbiter Ion Mass Spectrometer measurements are presented. There is a strong inbound-outbound difference in both the number and intensity of the superthermal ions with most events detected on the inbound crossing of the ionopause. The ambient energy of the detected ions is comparable to the ram energy of cold ions relative to the moving spacecraft. A comparison of the locations of the superthermal O(+) ion occurrences with respect to other parameters shows that the superthermals are a characteristic of the ionopause transition separating the essentially stationary ionosphere plasma from the flowing ionosheath plasma as deduced by Taylor et al. (1980) from individual examples.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; E5; p. 9055-9064.
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  • 2
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    Cosmogenic Al-26 and Na-22 in Luna-16 lunar regolith (1974)
    In:  CASI
    Details
    Publication Date: 2006-01-11
    Description: The activities of cosmogenic isotopes Al-26 and Na-22 in two samples taken from different depths of the lunar regolith core returned by the Luna 16 automatic station were measured by scintillation gamma spectrometer. The measured activities, when recalculated to the time of sampling of the lunar surface material, are: Al-26 - 62 + or - 8 and 54 + or - 9; Na-22 - 42 + or - 8 and 48 + or - 9. Depthwise distributions of the activities of these isotopes in lunar rocks of different types indicate the presence of a considerable depth gradient of activity near the surface caused by the fall off in the fluxes of primary and secondary cosmic radiation. The absence of this gradient in the measured samples, along with data on the tracks and content of inert gases, as well as the granulometric characteristics of the regolith indicate that the surficial layer of the regolith at the sampling site underwent mixing.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Soil from the Sea of Fertility (NASA-TT-F-15881); p 358-369
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  • 3
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    Granulometric characteristics of lunar surface material from the Sea of Fertility (1974)
    In:  CASI
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    Publication Date: 2006-01-11
    Description: The particle size distributions in the 1-1000 micrometer range along the length of the core of lunar surface material returned by Luna 16 were recorded by electrical impulse as well as sieve methods. The measurements are represented in the form of cumulative functions of the logarithm of size versus the logarithm of particle number, and also as the logarithm of size versus particle mass on a probability scale. The former functions at all depths consist of the super-positioning of two straight lines with slopes from 2.10 to 4.05. The second functions are near linear, which together with the closeness of the calculated asymmetries of the distribution to zero and the nearness of the calculated excess of the distributions to unity indicate the closeness of the recorded distributions to the logarithmically normal law. This agrees with the assumption that regolith particles were formed in a process of intensive mechanical grinding.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Soil from the Sea of Fertility (NASA-TT-F-15881); p 51-60
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  • 4
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    Box for working with lunar samples in nitrogen atmosphere (1974)
    In:  CASI
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    Publication Date: 2006-01-11
    Description: The design and equipment of a box specially built for working with lunar surface material is described. The box is intended for preliminary investigations, packing of samples, and carrying out a large number of operations necessary for this stage in the study of samples.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Soil from the Sea of Fertility (NASA-TT-F-15881); p 34-39
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  • 5
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    A reconsideration of the effects of terminator ionopause height on the nightward ion transport at Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The ionopause altitude near the terminator is a crucial parameter for studies dealing with the maintenance of the nightside ionosphere of Venus. It is generally thought that, during high solar wind dynamic pressures (P(SW)) or during solar minimum conditions, the ionopause comes down to very low altitudes so that the dayside ionosphere is not able to supply sufficient plasma to maintain the observed nightside densities. However, there are a number of workable definitions of the ionopause. Near the terminator, the altitude of the ionopause differs considerably depending upon the definition. The ionopause deduced from the radio occultation experiment as well as the pressure ionopause can be significantly lower than the density ionopause deduced from the Langmuir probe at these locations. The latter refers to the altitude where the electron density falls to 100/cu cm. Using in situ data from the Pioneer Venus Orbiter, it is shown that the density ionopause remains fairly high even for high P(SW) conditions. Simple quantitative estimates indicate that significant flow of plasma is still possible under these conditions. Thus, nightward transport of plasma during high P(SW) conditions may be more efficient than has been assumed so far. Since such conditions are more prevalent during solar cycle minimum, it is argued that transport may be relevant in the maintenance of nightside ionosphere at that time also.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A9, S; 13
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  • 6
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    Viscous shock layer analysis of the Martian aerothermal environment (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 29; 5; p. 633-640.
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  • 7
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    On the response of exospheric temperature on Venus to solar wind conditions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Exospheric temperatures, T(ex), inferred from in situ measurements of neutral densities by the Pioneer Venus Orbiter have been analyzed to examine any possible dependence on solar wind dynamic pressure, P(sw). No linear relationship was found between P(sw) and T(ex). However, on one occasion when P(sw) was unusually high for a prolonged period, an unmistakable temperature enhancement was observed. Minor enhancement of T(ex) were also observed in few other cases, with sustained but moderately high P(sw).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 7901-790
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  • 8
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    What maintains the zonal circulation in planetary atmospheres? (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The latest Voyager observations have shown large zonal velocities in Neptune's atmosphere, with some indication of alternating jets. Similar wind velocities have also been observed on Venus and are characteristic of planetary atmospheres in general, which is remarkable considering that the available solar or internal heating varies by more than a factor of 1000. A simplified model of the planetary circulation which provides some qualitative understanding is discussed. The basic assumption is that the source driving the circulation is also generating the dissipating eddies which are simulated by diffusion. Thus, the magnitude and structure of the zonal circulation are independent both of the source and the dissipation rate. The zonal velocities are related to the speed of sound and are of comparable magnitude in different atmospheres; although the available heating varies by a large factor, and the planetary parameters vary over a wide range. The alternating jets are described by a convective eigenmode which develops when energy transport out of the planetary interior is important, as is the case on Jupiter, Neptune, and Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 367; 361-366
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  • 9
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    Inter- and intra-group compositional variations in Apollo 15 pyroclastic green glass - An electron- and ion-microprobe study (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on major- and trace-element abundance analyses of Apollo 15 pyroclastic green glasses from groups A, B, C, D, and E, carried out using electron- and ion-microprobe techniques. The diagrams depicting Sr, Zr, Ba, and Nd vs Co variations indicate the presence of a high-Co trend in groups A and D and a low-Co trend in groups B and C. Group-E glasses were found to be significantly enriched in Sr, relative to the other four glass groups. Chemical data of this study were integrated with previous data to evaluate various magmatic processes that have been proposed in the past to explain chemical variations in the lunar green glass. Results of calculations using a source mixing model suggest that the Apollo 15 green glasses represent multiple eruptive events from three chemically distinct but compositionally variable source regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2565-257
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  • 10
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    Mars ionopause during solar minimum - A lesson from Venus (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ion densities measured by the Viking landers (Hanson et al., 1977) do not show an abrupt falloff with height, giving the false impression that Mars has no ionopause. On the basis of knowledge gained from the solar wind interaction at Venus during solar minimum, it is demonstrated that the observed O2 profile above about 160 km on Mars is a distributed photodynamical ionosphere and can produce an ionopause at around 325 km, similar to that observed on Venus during solar minimum. It is concluded that the solar wind interacts directly with the Mars ionosphere, suggesting that the planet does not have an intrinsic magnetic field of any consequence.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 8265-826
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