Constraints on Mimas’ interior from Cassini ISS libration measurements

• DOI: 10.1126/science.1255299
• Publication Date: 2014-10-16T18:23:02Z
• Authors: R. Tajeddine; N. Rambaux; V. Lainey; S. Charnoz; A. Richard; A. Rivoldini; B. Noyelles
• Keywords: Libration (molecule); Hydrostatic equilibrium; Enceladus; Tidal locking; Rotational dynamics; Orbit (dynamics)

Like our Moon, the majority of solar system's satellites are locked in a 1:1 spin-orbit resonance; on average, these show same face toward planet at constant rotation rate equal to satellite's orbital rate. In addition uniform rotational motion, physical librations (oscillations about an equilibrium) also occur. The may contain signatures internal properties. Using stereophotogrammetry Cassini Image Science Subsystem (ISS) images, we measured longitudinal forced Saturn's moon Mimas. Our measurements confirm all libration amplitudes calculated from dynamics, with one exception. This amplitude depends mainly Mimas' structure and has observed value twice predicted one, assuming hydrostatic equilibrium. After considering various possible interior models Mimas, argue that satellite either large nonhydrostatic interior, or ocean beneath thick icy shell.