NASA: Jupiter's Largest Moon Has a Salty Subterranean Ocean

PHOTO: The moon Ganymede orbits the giant planet Jupiter.NASA/ESA
In this artist’s concept, the moon Ganymede orbits the giant planet Jupiter. NASA’s Hubble Space Telescope observed aurorae on the moon generated by Ganymede’s magnetic fields. A saline ocean under the moon’s icy crust best explains shifting in the auroral belts measured by Hubble.

Ganymede, the largest moon in the solar system, is home to a salty ocean with more water than all the water on Earth, NASA said today.

While the moon, which orbits Jupiter, has long been suspected to contain water, the Hubble Space Telescope has found compelling evidence of a vast salt water ocean beneath the moon's icy surface, the space agency said.

Ganymede is the only moon in the solar system known to have its own magnetic field, and that magnetic field creates ribbons of glowing electrified gas, like the aurora on Earth. Scientists observed that when Jupiter's magnetic field changes, Ganymede's glowing ribbons of gas also changed -- rocking back and forth.

The changes in the aurorae allowed scientists to determine that a large amount of water is beneath Ganymede's surface affecting the moon's 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," Joachim Saur, a co-author of the study, said in a statement.

The ocean is believed to be buried under 95 miles of ice. Scientists estimated the ocean is 60 miles thick, making Ganymede's ocean ten times deeper than any ocean found on Earth, even though Ganymede itself has a radius that is about four-tenths that of the Earth.

Perhaps most exciting of all -- the discovery hints at the possibility that there could be a home for life beyond Earth.