Scientists using instruments aboard the Cassini spacecraft, have measured the wobbles of Mimas, the closest of Saturn's regular moons, and observed that the back and forth wobble caused a surface displacement of 6 kilometers.
Also they found that the amount of the to-and-fro motion indicated that Mimas' interior was not uniform and those wobbles could be produced if the moon contained a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its icy shell.
The astronomy team used a technique called stereo-photogrammetry to interpret images taken by the Cassini Imaging Science Subsystem to measure the libration.
Mimas, about 400 kilometers in diameter has a possible internal global ocean that is located under an icy crust ranging in thickness between 25 and 30 kilometers.
Radwan Tajeddine, the author said that the odd-shaped core would favor gravitational flattening by nearby Saturn, and the moon's relatively smooth and roughly spherical icy surface covered up whatever is underneath.
The study was published the findings in the journal Science.
