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  • 1980-1984  (21)
  • 1
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    Radar observations of asteroid 1685 Toro (1983)
    Institute of Physics
    Details
    Publication Date: 1983-04-01
    Print ISSN: 0004-6256
    Electronic ISSN: 1538-3881
    Topics: Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 2
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    Radar detection of Vesta (1980)
    Elsevier
    Details
    Publication Date: 1980-08-01
    Print ISSN: 0019-1035
    Electronic ISSN: 1090-2643
    Topics: Physics
    Published by Elsevier
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    PAPER CURRENT
  • 3
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    Radar properties of Europa, Ganymede, and Callisto (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The radar properties of Europa, Ganymede, and Callisto are summarized and present understanding of these properties is documented. The radar techniques are described, observational results reviewed, and salient aspects of the radar data set discussed. Theoretical interpretation of the satellites' anomalous radar properties is addressed, including aspects such as external scattering and double reflection from hemispherical craters, the random-facet model, total internal reflection, multiple total internal reflection, the high radar geometric albedos, the tenous upper layer, the two-component regolith, and compositional effects. It is concluded that multiple total internal reflection from randomly oriented subsurface facets can explain the anomalous circular polarization inversion in the radar echoes from the three satellites. Several refinements of the Goldstein-Green (1980) scattering model are suggested.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Radar Investigations of Asteroids (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Radar investigations of asteroids, including observations during 1984 to 1985 of at least 8 potential targets and continued analyses of radar data obtained during 1980 to 1984 for 30 other asteroids is proposed. The primary scientific objectives include estimation of echo strength, polarization, spectral shape, spectral bandwidth, and Doppler shift. These measurements yield estimates of target size, shape, and spin vector; place constraints on topography, morphology, density, and composition of the planetary surface; yield refined estimates of target orbital parameters; and reveals the presence of asteroidal satellites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-175348 , NAS 1.26:175348
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Radar observations of asteroid 1685 Toro (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The present results of 13 cm wavelength radar observations of the asteroid 1685 Toro, conducted at the Arecibo Observatory in July 1980, yield radar spectra which reveal correlated and approximately twofold variations in radar cross section and spectral bandwidth as functions of rotational phase, with two maxima and two minima per rotation cycle. In combination with the photopolarimetric results of Dunlap et al. (1973), the observations presently reported offer constraints on Toro's size, shape, and surface properties. Modeling Toro as a homogeneously scattering ellipsoid yields weighed least squares estimates for the lengths of the equatorial semiaxes and a nearly Lambertian scattering law.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 88; April 19
    Format: text
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  • 6
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    Radar observations of the icy Galilean satellites (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is shown that when combined with previous observations, 12.6 cm radar observations of Europa, Ganymede and Callisto made at the Arecibo Observatory in November 1977 and February 1979 firmly establish the distinguishing radar properties of the satellites: (1) high geometric albedos, (2) circular polarization ratios which anomalously exceed unity, (3) linear polarization ratios of approximately 0.5, and (4) diffuse scattering, which varies with the cosine of the angle of incidence. The weighted-mean values of these properties are tabulated, and it is found that although significant albedo and/or polarization features are common in the radar spectra, the fractional root mean square fluctuations in disk-integrated properties is only about 10%.
    Keywords: ASTRONOMY
    Format: text
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  • 7
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    Delay-Doppler radar observations of Saturn's rings (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Delay-Doppler observations at 12.6 cm which have been used to estimate the relative radar reflectivities of Saturn's classical ring sections show that the A and B rings are responsible for most of the radar echo, and that the average radar reflectivity per unit of projected area of the A ring is 90% as large as the B ring. No firm evidence is found for radar backscattering from particles interior to the B ring, exterior to the A ring, of from the planet itself. Unexpectedly large amounts of power at Doppler shifts near the center of the echo spectrum, which had been reported at 3.5 and 12.6 cm for ring plane tilt angles greater than 24.4 deg are not apparent in spectra for those wavelengths obtained at ring plane tilt angles smaller than 21.4 deg.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 49; Mar. 198
    Format: text
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  • 8
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    Comet Encke - Radar detection of nucleus (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The nucleus of the periodic comet Encke was detected in November 1980 with the Arecibo Observatory's radar system (wavelength, 12.6 cm). The echoes in the one sense of circular polarization received imply a radar cross section of 1.1 + or - 0.7 sq km. The estimated bandwidth of these echoes combined with an estimate of the rotation vector of Encke yields a radius for the nucleus of 1.5 +2.3 or -1.0. The uncertainties given are dependent primarily on the range of models considered for the comet and for the manner in which its nucleus backscatters radio waves. Should this range prove inadequate, the true value of the radius of the nucleus might lie outside the limits given.
    Keywords: ASTRONOMY
    Type: Science; 216; Apr. 16
    Format: text
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  • 9
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    Glass on the surfaces of Io and Amalthea (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of laboratory tests of the spectral reflectances of sulfur and sulfur-silicate glasses are compared with Voyager UV and IR spectral data of Io and Amalthea. Sulfur glasses, without the S8 allotrope, are formed when molten sulfur is quickly quenched to temperatures below 150 K. The trials involved heating sulfur to temperatures from 430-700 K, then quenching and recording the color that resulted. It was observed that the insulating properties of sulfur are so high that the glasses would probably only form in volcanic plumes, yielding particles in the 10-100 micron diameter range. Fumarole droplets could impact cold ground and leave 1 mm glass particles. Basalt-sulfur specimens heated to 1400 K to melt the basalt, then cooled, produced glasses of a color which matches the color of darker areas detected on Io. The surface colors of Amalthea, although definitely contaminated with particles from Io mass loss, exhibited only a few color matches with the basalt-sulfur glasses. More refined spectra of Amalthea are required if the surface constituents are to be identified.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Non-Crystalline Solids (ISSN 0022-3093); 67; 421-432
    Format: text
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  • 10
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    Ellipsoids and lightcurves (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The determination of the light curve (LC) of a geometrically scattering ellipsoid is considered in relation to the problem of investigating the physical properties of asteroids. A simple concise formula is derived for the area of a projection of an ellipsoid, and this expression is used to obtain a general formula for the projected, visible, illuminated area of a triaxial ellipsoid for arbitrary sun-earth-asteroid geometry. It is found that the LC of an ellipsoid has special properties that can be exploited to test the hypothesis that a given optical or radar LC could be due to a geometrically scattering ellipsoid.
    Keywords: ASTRONOMY
    Type: Geometriae Dedicata (ISSN 0046-5755); 17; 87-98
    Format: text
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