In 2015, after a nine-and-a-half-year journey, NASA’s New Horizons spacecraft raced past Pluto, beaming images of the dwarf planet back to Earth.

Five years after the mission, researchers are poring over images of Pluto’s far-side, which was shrouded in shadow during New Horizon’s flypast. They hope that these images will help give a better understanding of how Pluto was born and even whether a hidden ocean resides beneath the world’s icy crust.

This is an audio version of our feature: Pluto’s dark side spills its secrets — including hints of a hidden ocean