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  • 1
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    Asteroid radar astrometry (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Measurements of time delay and Doppler frequency are reported for asteroid-radar echoes obtained at Arecibo and Goldstone during 1980-1990. Radar astrometry is presented for 23 near-earth asteroids and three mainbelt asteroids. These measurements, which are orthogonal to optical, angular-position measurements, and typically have a fractional precision between 10 to the -5th and 10 to the -8th, permit significant improvement in estimates of orbits and hence in the accuracy of prediction ephemerides. Estimates are also reported of radar cross-section and circular polarization ratio for all asteroids observed astrometrically during 1980-1990.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 102; 1490-150
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  • 2
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    Mainbelt asteroids - Dual-polarization radar observations (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Observations of 20 asteroids in the main belt between Mars and Jupiter provide information about the nature of these objects' surfaces at centimeter-to-kilometer scales. At least one asteroid (Pallas) is extremely smooth at centimeter-to-meter scales. Each asteroid appears much rougher than the moon at some scale between several meters and many kilometers. The range of asteroid radar albedos is very broad and implies substantial variations in porosity or metal concentration (or both). The highest albedo estimate, for the asteroid Psyche, is consistent with a surface having porosities typical of lunar soil and a composition nearly entirely metallic.
    Keywords: ASTRONOMY
    Type: Science (ISSN 0036-8075); 229; 442-446
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  • 3
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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
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  • 4
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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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  • 5
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    Radar detection of Vesta (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Asteroid 4 Vesta was detected on November 6, 1979 with the Arecibo Observatory's S-band (12.6-cm-wavelength) radar. The echo power spectrum, received in the circular polarization opposite to that transmitted, yields a radar cross section of (0.2 + or - 0.1)pi a-squared, for a = 272 km. The data are too noisy to permit derivation of Vesta's rotation period.
    Keywords: ASTRONOMY
    Type: Icarus; 43; Aug. 198
    Format: text
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  • 6
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    Radar images of asteroid 1627 Ivar (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Radar echoes from the near-earth asteroid 1627 Ivar, whose orbit crosses the earth's, reveal it to be about twice as long as it is wide, with a maximum dimension no less than 7 km and probably within 20 percent of 12 km. The surface is fairly smooth at centimeter-to-meter scales but appears irregular and nonconvex at kilometer scales.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 99; 2012-201
    Format: text
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