What's going on inside Saturn's moon Mimas?
“The data suggest that something is not right, so to speak, inside Mimas,” said Radwan Tajeddine, a Cornell University research associate analysing the many images sent back by NASA's Cassini spacecraft. “The amount of wobble we measured is double what was predicted.”
Either possibility is intriguing, Tajeddine, lead author of a study published in Science, says.
If the battered surface of Mimas masks an ocean, it would join an exclusive club of “ocean worlds” that includes several moons of Jupiter and two other Saturn moons, Enceladus and Titan.
But Tajeddine says that is the less-likely scenario, as the surface of Mimas does not display signs of geologic activity.
On the other hand, an elongated frozen core would also be surprising. At more than four billion years old, Mimas' core should have relaxed into a more or less spherical shape. If instead it is oblong Tajeddine says it is likely to represent a record of the moon’s formation, frozen in time.
Models developed by Tajeddine and co-authors from France and Belgium indicate that, if the 396 kilometre-wide Mimas is hiding a liquid water ocean, it lies 24 to 31 kilometres beneath the surface.