The enigma of the Uranian satellites' orbital eccentricities
Abstract
Using recently published determinations of the diameters and orbital elements of the uranian satellites and assuming reasonable dissipation functions and rigidities for icy satellites, the eccentricity decay times for the satellites were calculated. For the inner three, decay times are on the order of 10 7-10 8 years, making it difficult to understand why these satellites still have their observed eccentricities. The three inner satellites have a near-commensurability in their mean motions that may be able to force their eccentricities at some time in the future, but cannot force them now. Several possible explanations exist: (1) The reported eccentricities are incorrect, and are in fact near-zero. (2) The reported mean motions are incorrect, and an exact commensurability exists. (3) The physical properties that we have assumed for the satellites are grossly in error (e.g., dissipation function Q is in reality very large). (4) The system is evolving very rapidly, perhaps from a previous state of higher eccentricity. Cases 1 and 2 are unlikely when one considers the quality of existing data. Case 3 would be more consistent with non-icy compositions. Cases 2 and 4 would imply some tidal heating of the satellites, particularly Ariel. A new lower bound of ∼ 1.7 × 10 4 on the Q of Uranus is calculated from the mass of Ariel and its proximity to Uranus.
- Publication:
-
Icarus
- Pub Date:
- February 1985
- DOI:
- 10.1016/0019-1035(85)90103-4
- Bibcode:
- 1985Icar...61..218S
- Keywords:
-
- Eccentric Orbits;
- Eccentricity;
- Natural Satellites;
- Oberon;
- Orbit Decay;
- Satellite Orbits;
- Uranus (Planet);
- Ariel;
- Error Analysis;
- Icy Satellites;
- Miranda;
- Orbital Elements;
- Physical Properties;
- Titania;
- Umbriel;
- URANUS;
- SATELLITES;
- ORBITS;
- ECCENTRICITY;
- PHYSICAL PROPERTIES;
- DECAY;
- CALCULATIONS;
- MOTION;
- CELESTIAL MECHANICS;
- COMMENSURABILITY;
- HYPOTHESES;
- TIDAL EFFECTS;
- ARIEL