Effect of Enceladus's rapid synchronous spin on interpretation of Cassini gravity
Abstract
Enceladus's degree 2 gravity, determined by Cassini, is nominally nonhydrostatic to 3σ (J2/C22 = 3.38-3.63, as opposed to 10/3). Iess et al. (2014) interpret this in terms of a hydrostatic interior (core) and isostatic (not hydrostatic) floating ice shell. Enceladus's rapid (1.37 d) synchronous spin and tide distorts its shape substantially, though, enough that the predicted hydrostatic J2/C22 is not 10/3 but closer to 3.25. This leads to the following revision to the internal picture of Enceladus, compared with Iess et al.: (1) the satellite's core is somewhat smaller and slightly denser (190 km radius and 2450 kg/m3); (2) the compensation depth (shell thickness) of the global (degree 2) ice shell is ≈ 50 km, rather close to the base of the modeled ice + water layer; and (3) the compensation depth (shell thickness) beneath the South Polar Terrain (from J3) remains shallower (thinner) at ≈ 30 km, independent of but influenced by the degree 2 solution.
- Publication:
-
Geophysical Research Letters
- Pub Date:
- April 2015
- DOI:
- 10.1002/2015GL063384
- Bibcode:
- 2015GeoRL..42.2137M
- Keywords:
-
- icy satellite;
- Cassini mission;
- gravity model;
- Enceladus ocean