So mark your calendar for the 16th June 2015 This is an awesome event itself but on this night you will have an amazing chance to view our celestial neighbors
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 rectangular pattern of gravity anomalies was completely unexpected. Using the gradients in the gravity data to reveal the rectangular pattern of anomalies, we can now clearly and completely see structures that were only hinted at by surface observations," Dr. Jeffrey Andrews-Hanna explained in the October 1, 2014 NASA Press Release. Dr. Andrews-Hanna, a GRAIL co-investigator at the Colorado School of Mines in Golden, Colorado, is lead author of the paper.