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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.08.014 Byline: Nicole J. Rappaport (a), Pierre-Yves Longaretti (b)(c), Richard G. French (d), Essam A. Marouf (e), Colleen A. McGhee (d) Keywords: Saturn; rings Abstract: Cassini radio science experiments have provided multiple occultation optical depth profiles of Saturn's rings that can be used in combination to analyze density waves. This paper establishes an accurate procedure of inversion of the wave profiles to reconstruct the wave kinematic parameters as a function of semi-major axis, in the nonlinear regime. This procedure is established using simulated data in the presence of realistic noise perturbations, to control the reconstruction error. It is then applied to the Mimas 5:3 density wave. There are two important concepts at the basis of this procedure. The first one is that it uses the nonlinear representation of density waves, and the second one is that it relies on a combination of optical depth profiles instead of just one profile. A related method to analyze density waves was devised by Longaretti and Borderies [Longaretti, P.-Y., Borderies, N., 1986. Icarus 67, 211-223] to study the nonlinear density wave associated with the Mimas 5:3 resonance, but the single photopolarimetric profile provided limited constraints. Other studies of density waves analyzing Cassini data [; Tiscareno, M.S., Burns, J.A., Nicholson, P.D., Hedman, M.M., Porco, C.C., 2007. Icarus 189, 14-34] are based on the linear theory and find inconsistent results from profile to profile. Multiple cuts of the rings are helpful in a fundamental way to ensure the accuracy of the procedure by forcing consistency among the various optical depth profiles. By way of illustration we have applied our procedure to the Mimas 5:3 density wave. We were able to recover precisely the kinematic parameters from the radio experiment occultation data in most of the propagation region; a preliminary analysis of the pressure-corrected dispersion allowed us to determine new but still uncertain values for the opacity (Ka0.02 cm.sup.2/g) and velocity dispersion of (c.sub.0a0.6cm/s) in the wave region. Our procedure constitutes the first step in our planned analysis of the density waves of Saturn's rings. It is very accurate and efficient in the far-wave region. However, improvements are required within the first wavelength. The ways in which this method can be used to establish diagnostics of ring physics are outlined. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, m.s. 301-150, 4800 Oak Grove Drive, Pasadena, CA 91109, USA (b) Universite Joseph Fourier, Laboratoire d'Astrophysique de Grenoble, BP 53, 38041 Grenoble Cedex 9, France (c) Centre National de la Recherche Scientifique (CNRS)/INSU, France (d) Astronomy Department, Wellesley College, Wellesley, MA 02181, USA (e) San Jose State University, One Washington Square, San Jose, CA 95192, USA Article History: Received 26 November 2007; Revised 11 July 2008; Accepted 19 August 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.03.025 Byline: Nicole J. Rappaport (a), Luciano Iess (b), Paolo Tortora (c), Aseel Anabtawi (a), Sami W. Asmar (a), Lucia Somenzi (b), Francesco Zingoni (b) Keywords: Saturn; satellites; Interiors Abstract: Gravity results are available from radio Doppler data acquired by the Deep Space Network during the encounter of the Cassini spacecraft with Enceladus in February 2005. We report the mass of Enceladus to be (1.0798[+ or -]0.0016)x10.sup.20kg, which implies a density of 1608.9[+ or -]4kgm.sup.-3. For a core made of hydrated silicates with a density of 2500 kgam.sup.-3 the core radius is [approximately equal to]190km and the quadrupole moment C.sub.22[approximately equal to]1.4x10.sup.-3. If Enceladus is in hydrostatic equilibrium, the larger than previously anticipated density implies that the recently proposed secondary spin-orbit resonance cannot be present. Therefore, the source of endogenic activity of Enceladus remains unexplained. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA (b) Dipartimento di Ingegneria Aerospaziale ed Astronautica, Universita' La Sapienza, I-00184 Rome, Italy (c) DIEM-II Facolta' di Ingegneria, Universita' di Bologna, I-47100 Forli, Italy Article History: Received 18 December 2006; Revised 12 March 2007

Abstract: The Cassini spacecraft encountered Rhea on November 26, 2005. Analysis of the Doppler data acquired at and around closest approach yields the mass of Rhea and the quadrupole moments of its gravity field with unprecedented accuracy. We obtained which corresponds to a density of . Our results for and are and , respectively. These values are consistent with hydrostatic equilibrium. From the value of , we infer the non-dimensional moment of inertia . Our models of Rhea''s interior based on the gravity data favor an almost undifferentiated satellite. A discontinuity between a core and a mantle is possible but not required by the data. Models with a constant silicate mass fraction throughout the body cannot account for the determined quadrupole coefficients. The data exclude fully differentiated models in which the core would be composed of unhydrated silicates and the mantle would be composed of pure ice. If the mantle contains 10% in mass of silicates, the core extends to 630 km in radius and has a silicate mass fraction of 40%. A continuous model in which the silicates are more concentrated toward the center of the body than in the outer layers is allowed by the gravity data but excluded by thermal evolution considerations. The one model that fits the gravity data and is self-consistent when energy transport and ice melting are qualitatively considered is an “almost undifferentiated” Rhea, in which a very large uniform core is surrounded by a relatively thin ice shell containing no rock at all. [Copyright &y& Elsevier]