HR: 14:40h
AN: P43B-05    [Abstracts]
TI: Cassini RADAR Observations of Phoebe
AU: * Ostro, S J
EM: ostro@reason.jpl.nasa.gov
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Elachi, C
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Anderson, Y
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Boehmer, R
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Callahan, P
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Hamilton, G
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Janssen, M
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Johnson, W
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Kelleher, K
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Lopes, R
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Roth, L
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Wall, S
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: West, R
AF: JPL/Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Allison, M
AF: NASA/Goddard, 2880 Broadway, New York, NY 10025 United States
AU: Kirk, R
AF: USGS, 2255 North Gemini Drive, Flagstaff, AZ 86001 United States
AU: Wood, C
AF: PSI, 1700 E. Ft. Lowell, Suite 106, Tucson, AZ 85719-2395 United States
AU: Posa, F
AF: Politechio di Bari, Via Amendola 173, Bari, 70126 Italy
AU: Stofan, E
AF: Proxemy Rsch., 12202 Raritan Lane, Bowie, MD 20715 United States
AU: Zebker, H
AF: Stanford U., STAR Laboratory, Stanford, CA 94305 United States
AU: Lorenz, R
AF: U. Arizona, Lunar & Planetary Laboratory, Tucson, AZ 85721 United States
AU: Lunine, J
AF: U. Arizona, Lunar & Planetary Laboratory, Tucson, AZ 85721 United States
AU: Francescetti, G
AF: U. Naples, Via Claudio, 21, Napoli, 80125 Italy
AU: Picardi, G
AF: U. Rome La Sapienza, Via Eudossiana 18, Rome, 00184 Italy
AU: Seu, R
AF: U. Rome La Sapienza, Via Eudossiana 18, Rome, 00184 Italy
AU: Muhleman, D
AF: Caltech, Geological & Planetary Sciences, Pasadena, CA 91125 United States
AU: Encrenaz, P
AF: DEMIRM/Obs. de Paris, 61, avenue de l'Observatoire, Paris, 75014 France
AB: The Cassini RADAR instrument, operating in its scatterometry mode, obtained continuous-wave (cw) echo power spectra from Phoebe during the inbound and outbound legs of the flyby, 4 h before and 2.5 h after closest approach. Phoebe's distance and subradar coordinates were approximately (93,000 km, 247 deg W, 26 deg S) inbound and (56,000 km, 323 deg W, 26 deg N) outbound. The durations of the cw sequences were 6 and 5 minutes. Larger intervals in the RADAR windows were devoted to observations with a chirp waveform able to provide range as well as Doppler resolution, and to passive radiometry; those data are not yet reduced. For Phoebe (and Dione, Mimas, Iapetus, Enceladus, Rhea, Hyperion, and Tethys), scatterometry aims to use estimates of radar albedo and angular scattering law to constrain the near-surface bulk density and/or the relative cleanliness of the icy regolith. The RADAR instrument's wavelength is 2.2 cm, vs. 3.5 cm or 13 cm for most groundbased radar astronomy, but Arecibo and Goldstone observations of the icy Galilean satellites and of asteroids give us no reason to expect significant wavelength dependence in this regime. Comparison of RADAR measurements of Titan and Iapetus with groundbased results will let us evaluate this expectation and will be key to calibrating both our measurements and their interpretation. Our inbound and outbound Phoebe echoes indicate Lambertian scattering, which requires structural complexity at scales no smaller than a centimeter. However, despite Phoebe's prominent large-scale topography, our spectra are nearly featureless, suggesting that the radar roughness is sub-topographic. We probably are seeing a combination of single scattering and multiple scattering from surface and subsurface structure. At this writing, our calibration indicates that Phoebe's average radar albedo is much closer to that of Iapetus than to those of the icy Galilean satellites.
DE: 6055 Surfaces and interiors
DE: 6062 Satellites
DE: 6275 Saturn
DE: 6280 Saturnian satellites
DE: 6949 Radar astronomy
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting