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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.
Science (New York, N.Y.)
|October 18, 2014
Summary
Saturn's moon Mimas exhibits physical librations that deviate from predictions, suggesting either a non-hydrostatic interior or a subsurface ocean. These findings offer new insights into the internal structure of icy moons.
Area of Science:
- Planetary Science
- Astrophysics
- Geophysics
Background:
- Most solar system satellites exhibit 1:1 spin-orbit resonance, showing a constant face toward their planet.
- Physical librations, or oscillations, in satellites may reveal internal properties.
- Saturn's moon Mimas is a key target for understanding satellite interiors.
Purpose of the Study:
- To measure the longitudinal physical forced librations of Mimas.
- To investigate Mimas' internal structure by analyzing libration amplitudes.
- To test models of Mimas' interior, including hydrostatic equilibrium and the presence of an ocean.
Main Methods:
- Stereophotogrammetry applied to Cassini Image Science Subsystem (ISS) images.
- Measurement of Mimas' longitudinal physical forced libration amplitudes.
- Comparison of observed amplitudes with predictions based on orbital dynamics and interior models.
Main Results:
- Observed libration amplitudes largely matched predictions, with one significant exception.
- The measured amplitude for one libration was twice the value predicted assuming hydrostatic equilibrium.
- This discrepancy points to Mimas' internal structure deviating from simple hydrostatic models.
Conclusions:
- Mimas' internal structure is likely significantly non-hydrostatic.
- Alternatively, Mimas may possess a hydrostatic interior with a substantial internal ocean beneath a thick icy shell.
- The librations of Mimas provide crucial constraints on its internal composition and evolution.
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