Satellite ``wakes'' and the orbit of the Encke Gap moonlet
Abstract
Quasiperiodic optical depth variations have been observed in the Voyager stellar (PPS) and radio occultation profiles near the Encke Gap of Saturn's rings, and have also been detected in one Voyager image. These fluctuations are believed to be the gravitational "wakes" of a moonlet orbiting within the gap. The existence of such a body had already been proposed by J. N. Cuzzi and J. D. Scargle (1985, Astrophys. J.292, 276-290) , based on radial "wavy edges" visible in numerous Voyager images of the gap. We develop a general model for these wakes, and use the results to estimate the moonlet's orbit and mass from the occultation data; this model may have broader applications to planetary rings. The moonlet longitude is best determined from the PPS scan interior to the gap, and is estimated to trail the observed profile by 32°. Considering the uncertainty caused by our neglect of particle collisions and self-gravity, the longitude is consistent with other estimates obtained from a second portion of the PPS scan exterior to the gap, and also from the radio profile. The moonlet orbits close to the center of the gap at an estimated semimajor axis of 133,603 ± 10 km; it has a mass of 5-10 × 10 -12 Saturn masses, which corresponds to a radius of ∼10 km if it is composed primarily of water ice. The consistency of the orbit parameters inferred from the PPS, radio, and wavy edge data virtually guarantees that a single dominant moonlet orbits within the gap.
- Publication:
-
Icarus
- Pub Date:
- May 1986
- DOI:
- 10.1016/0019-1035(86)90160-0
- Bibcode:
- 1986Icar...66..297S
- Keywords:
-
- Astronomical Models;
- Optical Thickness;
- Satellite Orbits;
- Saturn Rings;
- Saturn Satellites;
- Brightness Distribution;
- Density Distribution;
- Mass Distribution;
- Stellar Occultation;
- Voyager Project