HR: 14:30h
AN: P13A-05    [Abstracts]
TI: Saturn Ring Temperature Roll-off at Submillimeter Wavelengths From Cassini CIRS Observations
AU: * Spilker, L J
EM: Linda.J.Spilker@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr. M/S 230-205, Pasadena, CA 91109 United States
AU: Pilorz, S H
EM: Stuart.H.Pilorz@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr. M/S 230-205, Pasadena, CA 91109 United States
AU: Wallis, B D
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr. M/S 230-205, Pasadena, CA 91109 United States
AU: Edgington, S G
EM: Scott.G.Edgington@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr. M/S 230-205, Pasadena, CA 91109 United States
AU: Brooks, S M
EM: Shawn.M.Brooks@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr. M/S 230-205, Pasadena, CA 91109 United States
AU: Pearl, J C
AF: Goddard Space Flight Center, NASA GSFC Code 693, Greenbelt, MD 20771 United States
AU: Flasar, F M
AF: Goddard Space Flight Center, NASA GSFC Code 693, Greenbelt, MD 20771 United States
AB: The Cassini Composite Infrared Spectrometer (CIRS) spatially resolved Saturn's main rings, measuring the spectrum over a broad range of wavelengths, in particular covering the submillimeter band between 100 microns and 0.5 mm. For each ring, fitting a blackbody curve to the CIRS thermal spectrum between 25 and 100 microns (400 and 100 cm^-1), and accounting for the ring opacities, we derived ring brightness temperatures that also accounted for the ring filling factor. Using the best fits to the CIRS spectra, we find that the roll-off in ring temperature occurs at ~ 200 microns (50 cm^-1) for each ring. We used these data to investigation the spectral location of the roll-off that occurs somewhere between mid-thermal and centimeter wavelengths. The CIRS measurements unambiguously reveal a trend in brightness temperature that is much less steep between 50 and 100 microns than has been reported from earth-based observations. This more gradual trend implies that the main rings are not dominated by particles smaller than ~1 millimeter because larger particles do not show any significant variation in emission over the 50 to 100 micron wavelength range. This conclusion is consistent with results from particle eclipse cooling and high phase angle Voyager imaging observations. The roll-off in temperature measured by CIRS is principally due to material properties of the ring particles that change dramatically in this region. This work was performed at JPL under contract with NASA.
DE: 6265 Planetary rings
DE: 6275 Saturn
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly