Subterranean ocean discovered on Ganymede

Chuck Bednar for redOrbit.com – @BednarChuck

New observations made using the Hubble Space Telescope have uncovered the best evidence to date that Jupiter’s largest moon, Ganymede, is home to an underground saltwater ocean.

In fact, the subterranean ocean may have more water than the entirety of Earth’s surface, and according to CNET, it is estimated to be approximately 60 miles thick (or 10 times deeper than the Mariana Trench, the deepest part of the Pacific Ocean).

[STORY: Ganymede could be home to 'club sandwich' of ice and water]

“This discovery marks a significant milestone, highlighting what only Hubble can accomplish,” John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate at the US space agency’s Washington DC headquarters, said in a statement on Thursday.

“In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system,” he added. “A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth.”

Joining the line-up

The discovery of liquid water is a crucial step in the search for places beyond our Earth that may be capable of supporting microbial life. Ganymede, the largest moon in the solar system, joins other nearby moons such as Europa, Saturn’s Enceladus and Titan, and the dwarf planet Ceres as destinations that contain ice or liquid water are potentially habitable.

[VIDEO: Geologic map of Ganymede ]

Ganymede is also the only moon in our solar system with its own magnetic field, which causes ribbons of hot, glowing electrified gas known as aurorae to appear in regions circling the moon’s north and south poles. Due to the moon’s proximity to Jupiter, it is also embedded in the planet’s magnetic field, and changes in that field also cause changes in Ganymede’s aurorae.

Monitoring the aurorae

By monitoring the back-and-forth rocking motion of the two aurorae, authors of a new Journal of Geophysical Research: Space Physics study were able to determine that a tremendous amount of saltwater exists deep beneath its crust, impacting its magnetic field. The scientists believe that the saltwater is buried beneath a 95-mile (150-kilometer) crust comprised mostly of ice.

Lead investigator Joachim Saur of the University of Cologne in Germany and his colleagues came up with the idea of using the Hubble telescope to learn more about the inside of Ganymede. They hypothesized that if a saltwater ocean were present, Jupiter’s magnetic field would create a secondary magnetic field in the ocean that could counter the planet’s field.

[STORY: Aurora dazzles astronauts onboard the space station]

The resulting “magnetic friction” would suppress the rocking of the aurorae, the research team explained. The ocean combats Jupiter’s magnetic field so forcefully that it reduces the rocking of the electrified gas ribbons to two degrees, instead of the six that would occur without the ocean.

“I was always brainstorming how we could use a telescope in other ways,” Saur explained. “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.”

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Source: http://www.redorbit.com/news/space/1113351932/subterranean-ocean-discovered-on-jupiters-moon-ganymede-031315/