HR: 14:15h
AN: P13A-04    [Abstracts]
TI: Cassini First Diametric Radio Occultation of Saturn's Rings
AU: * Marouf, E
EM: emarouf@email.sjsu.edu
AF: San Jose State University, Electrical Engineering Department, San Jose, CA 95192-0084 United States
AU: French, R
EM: rfrench@wellesley.edu
AF: Wellesley College, Astronomy Department, Wellesley, MA 02181 United States
AU: Rappaport, N
EM: Nicole.J.Rappaport@jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Kliore, A
EM: Arvydas.J.Kliore@jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Flasar, M
EM: mike@leprss.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Laboratory for Extraterrestrial Physics, Greenbelt, MD 20771 United States
AU: Nagy, A
EM: anagy@umich.edu
AF: University of Michigan, Space Research Building, Ann Arbor, MI 48109 United States
AU: Ambrosini, R
EM: ambrosini@ira.cnr.it
AF: Institute of Radio Astronomy, Via Gobetti 101, Bologna, 40129 Italy
AU: McGhee, C
EM: cmcghee@wellesley.edu
AF: Wellesley College, Astronomy Department, Wellesley, MA 02181 United States
AU: Schinder, P
EM: schinder@leprss.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Laboratory for Extraterrestrial Physics, Greenbelt, MD 20771 United States
AU: Anabtawi, A
EM: Aseel.Anabtawi@jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Barbinis, E
EM: Elias.Barbinis@jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Goltz, G
EM: Gene.L.Goltz@jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Thomson, F
EM: fthomson@stanford.edu
AF: Stanford University, STAR Lab, EE Packard Building, Stanford, CA 94305 United States
AU: Wong, K
EM: wong_inbox@yahoo.com
AF: San Jose State University, Electrical Engineering Department, San Jose, CA 95192-0084 United States
AB: We present preliminary results expected from the first planned Cassini radio occultation observation of Saturn's rings, to be conducted on May 3rd, 2005. The path of Cassini as seen from Earth (the occultation track) has been designed to cross the rings from the west to the east ansa almost diametrically, allowing for occultation of all major ring features at two widely separated longitudes (about 180 deg apart). The duration of the geometric occultation is about 1.5 hours on each side. During the occultation, Cassini transmits through the rings three coherent monochromatic radio signals of wavelength 0.94, 3.6, and 13 cm (Ka-, X-, and S-band respectively), a capability unique to Cassini. The perturbed signals received at the Earth are recorded at the NASA DSN complexes at Goldstone and Canberra. Both direct and forward-scattered components of the signal may be identified in spectrograms of the received signals. The time history of the extinction of the direct signal is expected to yield high-spatial-resolution optical depth and phase shift profiles of ring structure. The timing of the occultation was optimized to allow probing the rings when the ring-opening-angle B (the angle between the line-of-sight and the ring plane) is relatively large (B = 23 deg), hence maximizing chances of measuring for the first time the structure of the relatively optically thick Ring B. In a similar experiment by Voyager in 1980, excessive signal attenuation along the long path within the nearly closed rings (B = 5.9 deg) limited the utility of the observations in relatively thick ring regions, in particular the main Ring B. For the Cassini optimized occultation geometry, a large B, slow radial velocity along the occultation track, and much improved phase stability of the reference ultrastable oscillator (USO) on board Cassini combine to promise achievable radial resolution approaching 100 m over a good fraction of the rings. Measurement of the amplitude and phase of the diffracted signal enables reconstruction of the observations to remove diffraction effects. Reliable high resolution profiling of ring structure at multiple ring longitudes is at the heart of investigating ring kinematics and dynamics, a major scientific objective of this experiment. In addition, observations of the scattered signal combined with measurements of the differential extinction of the three radio signals are expected to yield complementary information about ring physical properties, including particle size distribution and thickness, another major scientific objective.
DE: 5464 Remote sensing
DE: 5465 Rings and dust
DE: 6265 Planetary rings
DE: 6275 Saturn
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly