Astronomers found that Mimas has an ocean underneath it’s surface by observing and modeling it’s orbit. They found a backwards precession in the moon’s orbit meaning the shape of the elliptical orbit rotates backwards. It was previously believed the core of Mimas was solid, but if that were true, the orbit would not have a precession. After additionaly modeling, the only explanation is that it must be filled with water under the surface.
Fascinating!
From Nature Vol 626.
