With the GRAIL data, the astronomers were able to map the gravity field both in and around over 1,200 craters on the lunar far side. This region--the lunar highlands--is our Moon's most heavily cratered, and therefore oldest, terrain. Heavily cratered surfaces are older than smoother surfaces that are bereft of craters. This is because smooth surfaces indicate that more recent resurfacing has occurred, erasing the older scars of impact craters.
Ganymede: Ganymede is both the largest moon of Jupiter, our Solar System's planetary behemoth, as well as the largest moon in our entire Solar system. Observations of Ganymede by the HST in 2015 suggested the existence of a subsurface saline ocean. This is because patterns in auroral belts and rocking of the magnetic field hinted at the presence of an ocean. It is estimated to be approximately 100 kilometers deep with a surface situated below a crust of 150 kilometers.
The team's findings can also be applied to exoplanets, which are planets that circle stars beyond our own Sun. Some super-Earth exoplanets, which are rocky planets more massive than our own, have been proposed as "water worlds" covered with churning oceans. Could they have life? Perhaps. The potential would certainly be there. Dr. Vance and his team believe laboratory experiments and more sophisticated modeling of exotic oceans might help to find answers to these very profound questions.