Geometry of the Saturn System from the 3 July 1989 Occultation of 28 Sgr and Voyager Observations

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

“…However, many of the images used in this study contain little sky and hence few stars on which to navigate, so we instead used known circular ring features and assigned these features the absolute radii determined from Voyager and 28 Sgr occultation data (French et al 1993).…”

“…In order to remove any systematic effects in the navigation of each data set, we used the known radii of circular features derived from the work of French et al (1993) to place all of our raw radius measurements on their radial scale, as in Porco et al (1984). The result is a radial position "scaled" relative to the absolute position of the fiducial features.…”

“…Based on our experience with the Cassini imaging data sets, we took 0.1 as the constant of proportionality between the measured feature width and the adopted uncertainty in the radial location of the edge. We also accounted for the 0.7 km uncertainty in the fiducial radii given in French et al (1993).…”

“…The only French et al (1993) fiducial feature available in every data set used in this work was the outer edge of the Keeler gap (feature number 1 in French et al 1993). However, we now know that near the longitude of the recently discovered satellite Daphnis ) the outer edge of the Keeler gap is perturbed, with an amplitude of about 2 km, so we did not use observations taken within 5…”

Exomoon Habitability Constrained by Illumination and Tidal Heating

“…Such simulations will also be necessary to simulate the long-term evolution of the orientation g of the moon's inclination i with respect to the periastron of the star-related orbit, because for significant eccentricities e Ãp it will make a big difference whether the summer of either the northern or southern hemisphere coincides with minimum or maximum distance to the star. Technically, these variations refer to the apsidal precession (the orientation of the star-related eccentricity, i.e., of a Ãp ) and the precession of the planet's rotation axis, both of which determine g. For Saturn, and thus Titan, the corresponding timescale is of order 1 Myr (French et al, 1993), mainly induced by solar torques on both Saturn's oblate figure and the equatorial satellites. Habitable exomoons might preferably be irregular satellites (see Section 2) for which Carruba et al (2002) showed that their orbital parameters are subject to particularly rapid changes, driven by stellar perturbations.…”