Related Experiment Video
Updated: Apr 22, 2026

Quantifying Intermembrane Distances with Serial Image Dilations
Published on: September 28, 2018
Constraints on Mimas' interior from Cassini ISS libration measurements
R Tajeddine1, N Rambaux2, V Lainey3
1Department of Astronomy, Cornell University, Ithaca, NY 14853, USA. IMCCE-Observatoire de Paris, UMR 8028 du CNRS, UPMC, Université Lille 1, 77 Av. Denfert-Rochereau, 75014 Paris, France. Université Pierre et Marie Curie, UPMC - Paris VI, 4 Place Jussieu, 75005 Paris, France. tajeddine@astro.cornell.edu.
Abstract:
Like our Moon, the majority of the solar system's satellites are locked in a 1:1 spin-orbit resonance; on average, these satellites show the same face toward the planet at a constant rotation rate equal to the satellite's orbital rate. In addition to the uniform rotational motion, physical librations (oscillations about an equilibrium) also occur. The librations may contain signatures of the satellite's internal properties. Using stereophotogrammetry on Cassini Image Science Subsystem (ISS) images, we measured longitudinal physical forced librations of Saturn's moon Mimas. Our measurements confirm all the libration amplitudes calculated from the orbital dynamics, with one exception. This amplitude depends mainly on Mimas' internal structure and has an observed value of twice the predicted one, assuming hydrostatic equilibrium. After considering various possible interior models of Mimas, we argue that the satellite has either a large nonhydrostatic interior, or a hydrostatic one with an internal ocean beneath a thick icy shell.
Related Concept Videos
Reduced Mass Coordinates: Isolated Two-body Problem
Magnetostatic Boundary Conditions
Trigonometric Substitution
Bending and Torsional Moments
The reaction developed in a structural element when subjected to an external force causes the element to bend. When a structural element bends upwards, it creates compressive normal forces on the top and tensile normal forces on the bottom, resulting in a couple that determines the bending...
Gravitation Between Spherically Symmetric Masses
Conservation of Mass in Fixed, Nondeforming Control Volume
In the case of a sewer pipe, which can be modeled...

