"Makemake is in the class of rare Pluto-like objects, so finding a companion is important. The discovery of the moon has given us an opportunity to study Makemake in far greater detail than we ever would have been able to without the companion," Dr. Parker continued to explain.
Since its discovery centuries ago, Ganymede has been the target of a great deal of well-deserved attention from the planetary science community. Earth-bound telescopes have gazed at Ganymede's puzzling, icy surface and, in later decades, flyby space missions and spacecraft, circling around Jupiter, have scrutinized Ganymede--trying to solve its numerous mysteries. These observations ultimately unveiled a complicated, icy moon-world, whose bizarre surface showed a strange and puzzling contrast between its two main types of terrain: the dark, extremely ancient and heavily cratered surface terrain, and the much younger--but still ancient--lighter terrain showing a vast array of mysterious grooves and ridges.
GRAIL has also generated new maps showing lunar crustal thickness. These maps have managed to uncover still more large impact basins on the near-side hemisphere of Earth's Moon--revealing that there are fewer such basins on the far-side, which is the side that is always turned away from Earth. This observation begs the question: How could this be if both hemispheres were on the receiving end of the same number of crashing, impacting, crater-excavating projectiles? According to GRAIL data, the answer to this riddle is that most of the volcanic eruptions on Earth's Moon occurred on its near-side hemisphere.