The Orbits of Saturn's Small Satellites Derived from Combined Historic andCassiniImaging Observations

Abstract

We report on the orbits of the small, inner Saturnian satellites, either recovered or newly discovered in recent Cassini imaging observations. The orbits presented here reflect improvements over our previously published values in that the time base of Cassini observations has been extended, and numerical orbital integrations have been performed in those cases in which simple precessing elliptical, inclined orbit solutions were found to be inadequate. Using combined Cassini and Voyager observations, we obtain an eccentricity for Pan 7 times smaller than previously reported because of the predominance of higher quality Cassini data in the fit. The orbit of the small satellite (S/2005 S1 [Daphnis]) discovered by Cassini in the Keeler gap in the outer A ring appears to be circular and coplanar; no external perturbations are apparent. Refined orbits of Atlas, Prometheus, Pandora, Janus, and Epimetheus are based on Cassini , Voyager, Hubble Space Telescope, and Earth-based data and a numerical integration perturbed by all the massive satellites and each other. Atlas is significantly perturbed by Prometheus, and to a lesser extent by Pandora, through high-wavenumber mean-motion resonances. Orbital integrations involving Atlas yield a mass of GM Atlas ¼ (0:44 AE 0:04) ; 10 À3 km 3 s À2, 3 times larger than reported previously (GM is the product of the Newtonian constant of gravitation G and the satellite mass M ). Orbital integrations show that Methone is perturbed by Mimas, Pallene is perturbed by Enceladus, and Polydeuces librates around Dione's L5 point with a period of about 791 days. We report on the nature and orbits of bodies sighted in the F ring, two of which may have persisted for a year or more.

Time Variability in the Outer Edge of Saturn's a-Ring Revealed by Cassini Imaging

“…According to this approximation, the satellite's semimajor axis should be Δa = 14300 ± 1500 km/3π = 1500 ± 160 km beyond the A-ring edge, well outside the orbit of Atlas (Δa 900 km) and well inside the orbit of Prometheus (Δa 2600 km; Spitale et al 2006). Although the pattern is localized in azimuth, the 6…”

“…The mass of Janus is ∼3.6 times that of Epimetheus (Spitale et al 2006), so at the nominal ring edge with a = 136,773 km (Porco et al 1984), Janus would be expected to induce a forced eccentricity in a test particle orbit nearly 2 orders of magnitude stronger than that from Epimetheus. Moreover, since the Janus resonance falls inside the ring, forced eccentricities from that resonance should be much larger still, limited only by inter-particle interactions.…”

Revised Orbits of Saturn's Small Inner Satellites

“…− 7 10 ± 5 9± 5 Nicholson et al (1992) 132.1 ± 8.3 36.7 ± 2.0 Jacobson (1996) 128.4 ± 6.0 35.7 ± 1.7 Renner, Sicardy & French (2004) 14.1 + 1.0 − 2.5 10.3 + 1.0 − 1.9 Jacobson & French (2004) 126.9 ± 0.9 35.2 ± 0.3 12.0 ± 0.7 10.1 ± 0.5 Spitale et al (2006) 126.58 ± 0.33 35.40 ± 0.09 0.44 ± 0.04 10.45 ± 0.13 9.05 ± 0.15 Current work 126.60 ± 0.08 35.13 ± 0.02 0.44 ± 0.03 10.64 ± 0.10 9.15 ± 0.13…”

“…Paper I (Spitale et al 2006) reported on the determination of orbits of the small inner Saturnian satellites, Janus, Epimetheus, Atlas, Prometheus, Pandora, Pan, Methone, Pallene, Polydeuces, and Daphnis, using Earth-based and Hubble Space Telescope astrometry and Voyager and Cassini imaging observations; the Cassini data arc extended through 2005 November. Since that time Cassini has continued to collect observations.…”

Symmetric horseshoe periodic orbits in the general planar three-body problem

“…In this particular system the new data provided by Cassini's observations has been useful to get more accurate computations of some relevant parameters of the Saturn's moons dynamics (Spitale et al 2006). The main theoretical results have been concerned with the threebody restricted models.…”