Saturn's moon Mimas may have ocean under its icy surface

A new study has suggested that the wobbles of Mimas, the closest of Saturn's regular moons, indicate that the moon either contains a weirdly shaped rocky core or has a sub-surface ocean beneath its icy shell.

Lead author Radwan Tajeddine from the Cornell University said that after carefully examining Mimas, they found that it librates, that is, it subtly wobbles around the moon's polar axis.

Tajeddine added that in physical terms, the back-and-forth wobble should produce about 3 kilometers of surface displacement, but they observed an unexpected 6 kilometers of surface displacement.

The astronomy team used a technique called stereo-photogrammetry to interpret images taken by the Cassini Imaging Science Subsystem to measure the librations.

The amount of the to-and-fro motion indicates that Mimas' interior is not uniform and these wobbles can be produced if the moon contains a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its icy shell.

Mimas is about 400 kilometers in diameter and its possible internal global ocean is located under an icy crust ranging in thickness between 25 and 30 kilometers.

The moon itself is thought to have been formed either by the slow agglomeration of ring particles (a gradual buildup of matter) or direct growth within the primordial planetary gas nebula and as per Tajeddine, the odd-shaped core would favor gravitational flattening by nearby Saturn.

The study is published in Science.