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  • 1
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    The surface abundance and stratigraphy of lunar rocks from data about their albedo (1977)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The data pf ground-based studies and surveys of the lunar surface by the Zond and Apollo spacecraft have been used to construct an albedo map covering 80 percent of the lunar sphere. Statistical analysis of the distribution of areas with various albedos shows several types of lunar surface. Comparison of albedo data for maria and continental areas with the results of geochemical orbital surveys allows the identification of the types of surface with known types of lunar rock. The aluminum/silcon and magnesium/silicon ratios as measured by the geochemical experiments on the Apollo 15 and Apollo 16 spacecraft were used as an indication of the chemical composition of the rock. The relationship of the relative aluminum content to the age of crystalline rocks allows a direct dependence to be constructed between the mean albedo of areas and the age of the rocks of which they are composed.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, pt. 1; p 253-258
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  • 2
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    Measurement of the optical properties of lunar rocks in the transition zone, resulting from observations made by Lunokhod 2 (1977)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Photometric measurements were carried out directly on the lunar surface with the aid of a calibration device, a plate with fields of different brightness, placed in the field of view of the panoramic telephotometers. The brightness of the fields of the calibration plate were measured in preliminary studies, relative to the brightness of a magnesia screen. This permitted determination of the reflectance features of the surficial lunar material relative to the standard most widely used in brightness studies of natural substances. The total brightness of sections a few centimeters across was recorded in direct proximity to the apparatus. The total area investigated in one panorama was about one square meter. Several areas in the mare and highland regions were studied. The albedos of various surface objects were obtained. A comparison of the brightness measurements with data from the RIFMA-M instrument discloses a correlation of the albedo change with change in chemical composition of the surface rock. Direct photometric studies of the lunar surface in the "mare-highland" transition zone assist in tracing the transition from one type of rock to another, and in obtaining information on the processes of material exchange between these two types of lunar landscape.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington The Soviet-Am. Conf. on Cosmochem. of the Moon and Planets, Pt. 2; p 763-767
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  • 3
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    A model of inner cometary ionospheres (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A hydrodynamical model to describe the movement of the thermalized charged components in the inner ionosphere of comet Halley is presented. Photoelectrons are included by applying a two-stream-type approach. The numerical scheme describes shock transitions in a natural way. Solutions are obtained for a number of different assumptions concerning electron heating rates but all show that the electron temperature increases sharply where the collisional electron neutral coupling becomes unimportant. This temperature increase is accompanied by an increase in the plasma pressure and in its associated polarization electric field, and causes the plasma flow to go subsonic. In certain cases this transition occurs as an inner shock which may explain the observed ion pile-up in Halley's comet.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 235-239
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  • 4
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    The solar wind interaction with Comet P/Grigg-Skjellerup (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The Giotto spacecraft is scheduled to intercept Comet P/Grigg-Skjellerup on July 10, 1992. The observed outgassing rate of this comet is over an order of magnitude smaller than Comet Giacobini-Zinner and over two orders of magnitude smaller than that of Comet Halley. Consequently, the new data obtained during the upcoming encounter will strengthen our understanding of how the solar wind interaction with comets depends upon the neutral gas production rate. In this brief note, we make predictions of the location of the flow transition regions - i.e., the bow shock and the ionopause, and discuss the expected level of wave turbulence.
    Keywords: ASTROPHYSICS
    Type: Earth, Moon, and Planets (ISSN 0167-9295); 60; 1; p. 31-40.
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  • 5
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    The sheath/ionosphere boundary layer at Venus (1995)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: At Venus the interaction of the shocked solar wind and cold planetary ions takes place in the dayside mantle. The shocked solar wind is a warm, drifting Maxwellian plasma whereas the planetary plasma is cold; the plasma in the mantle is strongly magnetized. The coexistence of these two populations is unstable, and it leads to wave excitations that organize the energy and momentum exchange between the shocked solar wind and the plasma of planetary origin. The source of the free energy is the solar wind. The intensive wave activity seen in the 100 Hz channel of the wave instrument onboard the Pioneer-Venus Orbiter in the dayside mantle region of Venus can be identified as almost electrostatic VLF waves excited by the kinetic branch of the modified two-stream lower hybrid instability. The waves interact with the particles, and the planetary plasma is heated and accelerated outside the ionosphere, close to its upper boundary. This way solar wind scavenges the ionosphere, and planetary ions leave the planetary magnetosphere. A portion of the wave energy is capable of penetrating directly into the ionosphere and heating it.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 4; p. (4)71-(4)74
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  • 6
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    Lower hybrid turbulence at cometary bow wave and acceleration of cometary protons (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The wave measurements at the spacecraft encounters with Comet Halley have shown intense wave activity at the lower hybrid frequency. The excitation of the lower hybrid instability by the pickup cometary ions (protons and water group) in the bow wave region and the quasi-linear diffusion of the ions in these fluctuations are discussed. The quasi-linear diffusion of the pickup protons takes place over a scale length shorter than that of the heavier water group ions. This enhances damping of the waves by protons, and when the pickup proton density is large enough, it can result in the saturation of the instability as this damping balances the heavy ion driven growth. The observed electric field amplitude and the scale length of proton relaxation are in agreement with the theory. For small pickup proton density the instability can saturate due to the wave energy cascade arising from the modulation instability of the large-amplitude lower hybrid waves. This saturation mechanism leads to electron acceleration and suprathermal tail formation.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A2; p. 1325-1331.
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