Among the many different layers of Jupiter moon Ganymede, scientists have determined an underground saltwater ocean lies in wait. The latest find was made by NASA’s Hubble Space Telescope, which observed subtle shifts in the moon’s aurorae. The find comes on the heels of news that Saturn’s icy moon Enceladus might also have its own subsurface ocean.

Ganymede has been suspected of concealing an ocean for decades—scientists first found evidence back in the 1970s—and this latest find confirms year’s worth of intense research. Even back in 2002, NASA’s Galileo mission found evidence to support the agency’s suspicions, though not enough to make a definitive confirmation.

Ganymede is our solar system’s largest moon, and the only moon with its own magnetic field, too. Because of these magnetic fields, ribbons of glowing gas (aurorae) are often seen circling the north and south poles of the moon, which are affected by the magnetic field of Jupiter. With the aurorae shifts, scientists were able to determine that a saltwater ocean exists beneath Ganymede’s surface, which also affects the moon’s magnetic field.

Joachim Saur of the University of Cologne in Germany explained how the idea to observe the aurorae came about.

“I was always brainstorming how we could use a telescope in other ways,” said Saur. “Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon’s interior.”

If an ocean does indeed exist, scientists estimate it’s about 60 miles thick, which is about 10 times deeper than the deepest ocean here on Earth. But you wouldn’t even know it if you were standing on the Jupiter moon; the ocean is said to be buried beneath a 95-mile-thick crust of pure ice. (I’d love to see the day when NASA drills through the crust and reaches the ocean.)

“A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth,” said NASA astronaut John Grunsfeld.