Waves in Cassini UVIS stellar occultations. 2. The C ring

Kévin Baillié (1) , Joshua Colwell (2) , Jack J Lissauer , Larry Esposito (3) , Miodrag Sremčević

1 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
2 UCF - University of Central Florida [Orlando]
3 LASP - Laboratory for Atmospheric and Space Physics [Boulder]

We performed a complete wavelet analysis of Saturn's C ring on 62 stellar occultation profiles. These profiles were obtained by Cassini's Ultraviolet Imaging Spectrograph High Speed Photometer. We used a WWZ wavelet power transform to analyze them. With a co-adding process, we found evidence of 40 wavelike structures, 18 of which are reported here for the first time. Seventeen of these appear to be propagating waves (wavelength changing systematically with distance from Saturn). The longest new wavetrain in the C ring is a 52-km-long wave in a plateau at 86,397 km. We produced a complete map of resonances with external satellites and possible structures rotating with Saturn's rotation period up to the eighth order, allowing us to associate a previously observed wave with the Atlas 2:1 inner Lindblad resonance (ILR) and newly detected waves with the Mimas 6:2 ILR and the Pandora 4:2 ILR. We derived surface mass densities and mass extinction coefficients, finding r = 0.22(±0.03) g cm À2 for the Atlas 2:1 ILR, r = 1.31(±0.20) g cm À2 for the Mimas 6:2 ILR, and r = 1.42(±0.21) g cm À2 for the Pandora 4:2 ILR. We determined a range of mass extinction coefficients (j = s/r) for the waves associated with resonances with j = 0.13 (±0.03) to 0.28(±0.06) cm 2 g À1 , where s is the optical depth. These values are higher than the reported values for the A ring (0.01-0.02 cm 2 g À1) and the Cassini Division (0.07-0.12 cm 2 g À1 from Colwell et al. (Colwell, J.E., Cooney, J.H., Esposito, L.W., Sremčević , M. [2009]. Icarus 200, 574-580)). We also note that the mass extinction coefficient is probably not constant across the C ring (in contrast to the A ring and the Cassini Division): it is systematically higher in the plateaus than elsewhere, suggesting smaller particles in the plateaus. We present the results of our analysis of these waves in the C ring and estimate the mass of the C ring to be between3.7(±0.9) Â 10 16 kg and 7.9(±2.0) Â 10 16 kg (equivalent to an icy satellite of radius between 28.0(±2.3) km and 36.2(±3.0) km with a density of 400 kg m À3 , close to that of Pan or Atlas). Using the ring viscosity derived from the wave damping length, we also estimate the vertical thickness of the C ring between 1.9(±0.4) m and 5.6(±1.4) m, comparable to the vertical thickness of the Cassini Division.

Domaines: Astrophysique [astro-ph]; Planétologie et astrophysique de la terre [astro-ph.EP]

Kévin Baillié, Joshua Colwell, Jack J Lissauer, Larry Esposito, Miodrag Sremčević. Waves in Cassini UVIS stellar occultations. 2. The C ring. Icarus, 2011, 216 (1), pp.292-308. ⟨10.1016/j.icarus.2011.05.019⟩. ⟨hal-02352150⟩