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Many objects in the solar system are suspected to have experienced reorientation of their spin axes. As their rotation rates are slow and their shapes are nearly spherical, the formation of mass anomalies, by either endogenic or exogenic processes, can change objects’ moments of inertia. Therefore, the objects reorient to align their largest moment of inertia with their spin axis. Such a phenomenon...
We analyze several thousand Cassini ISS images in order to study the inner edge of the Keeler gap in Saturn's outer A ring. We find strong evidence for an m = 32 perturbation with a mean amplitude of radial variation of 4.5km. Phase analysis yields a pattern speed consistent with the mean motion of Prometheus, indicating that this pattern is generated by the 32:31 Inner Lindblad resonance with Prometheus...
We present a study of the behavior of Saturn’s A ring outer edge, using images and occultation data obtained by the Cassini spacecraft over a period of 8years from 2006 to 2014. More than 5000 images and 170 occultations of the A ring outer edge are analyzed. Our fits confirm the expected response to the Janus 7:6 Inner Lindblad resonance (ILR) between 2006 and 2010, when Janus was on the inner leg...
We present observations at optical wavelengths with the Cassini Spacecraft’s Imaging Science System of the Phoebe ring, a vast debris disk around Saturn that seems to be collisionally generated by its irregular satellites. The analysis reveals a radial profile from 80–260 Saturn radii (RS) that changes behavior interior to ≈110RS. We attribute this to either the moon Iapetus...sweeping up small particles,...
The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35° across, and a wide-angle refractor...
The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35° across, and a wide-angle refractor...
The Phoebe ring, Saturn’s largest and faintest ring, lies far beyond the planet’s well-known main rings. It is primarily sourced by collisions with Saturn’s largest irregular satellite Phoebe, perhaps through stochastic macroscopic collisions, or through more steady micrometeoroid bombardment. The ring was discovered with the Spitzer Space Telescope at 24μm and has a normal optical depth of ∼2×10...
We respond to Klačka et al. (Klačka, J., Petržala, J., Pástor, P., Kómar, L. [2014]. Icarus, this issue, http://dx.doi.org/10.1016/j.icarus.2012.06.044.), who have criticized many previous derivations of the acceleration experienced by a spherical interplanetary particle owing to the Sun’s radiation. Much of their criticism arises from differences in semantics and notation as well as effects that...
Dust grains generated by the Uranian irregular satellites will undergo chaotic large-amplitude eccentricity oscillations under the simultaneous action of radiation forces and the highly misaligned quadrupole potentials of the oblate planet and distant Sun. From a suite of orbital histories, we estimate collision probabilities of dust particles with the regular satellites and argue that this process...
The Iapetus −1:0 nodal bending wave, the first spiral wave ever described in Saturn’s rings, has been seen again for the first time in 29years. We demonstrate that it is in fact the nodal bending wave, not the 1:0 apsidal density wave as previously reported. We use wavelet analysis to determine the wavelength profile, thus deriving the surface density at every point in the region covered by the bending...
Images taken by the Cassini spacecraft display numerous “propellers”, telltale disturbances detected in Saturn’s outer A ring. In conventionally accepted models (Seiß, M., Spahn, F., Sremčević, M., Salo, H. [2005]. Geophys. Res. Lett. 32, L11205; Lewis, M., Stewart, G. [2009]. Icarus 199, 387–412), unseen moonlets are considered to generate these structures by gravitationally stirring the shearing...
The leading face of Saturn’s moon Iapetus, Cassini Regio, has an albedo only one tenth that on its trailing side. The origin of this enigmatic dichotomy has been debated for over 40years, but with new data, a clearer picture is emerging. Motivated by Cassini radar and imaging observations, we investigate Soter’s model of dark exogenous dust striking an originally brighter Iapetus by modeling the dynamics...
High-resolution images from the Cassini Imaging Science Subsystem (ISS) show parallel sets of grooves on Epimetheus and Pandora. Grooves have previously been observed on other satellites and asteroids, including Phobos, Gaspra, Ida, Eros, and minor occurrences on Phoebe. Sets of parallel grooves are so far observed only on satellites known or likely to be subject to significant tidal stresses, such...
Epimetheus, a small moon of Saturn, has a rotational libration (an oscillation about synchronous rotation) of 5.9°±1.2°, placing Epimetheus in the company of Earth’s Moon and Mars’ Phobos as the only natural satellites for which forced rotational libration has been detected. The forced libration is caused by the satellite’s slightly eccentric orbit and non-spherical shape.Detection of a moon’s forced...
Many asteroids are thought to be particle aggregates held together principally by self-gravity. Here we study — for static and dynamical situations — the equilibrium shapes of spinning asteroids that are permitted for rubble piles. As in the case of spinning fluid masses, not all shapes are compatible with a granular rheology. We take the asteroid to always be an ellipsoid with an interior modeled...
We present a comprehensive examination of Jupiter's “gossamer” rings based on images from Voyager, Galileo, the Hubble Space Telescope and the W.M. Keck Telescope. We compare our results to the simple dynamical model of Burns et al. [Burns, J.A., Showalter, M.R., Hamilton, D.P., Nicholson, P.D., de Pater, I., Ockert-Bell, M., Thomas, P., 1999. Science 284, 1146–1150] in which dust is ejected from...
We describe a powerful signal processing method, the continuous wavelet transform, and use it to analyze radial structure in Cassini ISS images of Saturn's rings. Wavelet analysis locally separates signal components in frequency space, causing many structures to become evident that are difficult to observe with the naked eye. Density waves, generated at resonances with saturnian satellites orbiting...
The Cassini spacecraft has provided the first clear images of the D ring since the Voyager missions. These observations show that the structure of the D ring has undergone significant changes over the last 25 years. The brightest of the three ringlets seen in the Voyager images (named D72), has transformed from a narrow, <40-km wide ringlet to a much broader and more diffuse 250-km wide feature...
We investigate planetary fly-bys of asteroids using an approximate volume-averaged method that offers a relatively simple, but very flexible, approach to study the rotational dynamics of ellipsoids. The asteroid is considered to be a deformable, prolate ellipsoid, with its interior being modeled as a rigid-granular material. Effects due to the asteroid's rotation, its self-gravity and gravitational...
The Yarkovsky force, produced when thermal radiation is re-emitted asymmetrically, causes significant orbital evolution of asteroids in the 10 m–10 km size range. When acting on a non-spherical body, the momentum carried by this radiation generally produces a torque, called the YORP effect, which may be important in re-orienting asteroidal spins. Here we explore a related effect, the “binary YORP”...
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