Ganymede has a saltwater ocean

NASA says new observations from the Hubble Space Telescope confirm the presence of a subsurface ocean on Jupiter's largest moon.

by Eric Mack

NASA says new observations from the Hubble Space Telescope confirm the existence of a salty subsurface ocean on Ganymede, the largest moon in the solar system, which orbits our largest neighbor planet, Jupiter.The ocean is estimated to be about 60 miles thick -- 10 times deeper than the Mariana Trench, the deepest part of the Pacific -- but is buried under a layer of mostly icy crust 95 miles thick. Ganymede joins other neighborhood moons like Europa, the asteroid belt dwarf planet Ceres, and Saturn's Enceladus and Titan that host strange icy or liquid layers, making them prime targets in the search for life beyond Earth.
Scientists have hypothesized for decades that Ganymede might harbor an icy or even liquid ocean beneath its frigid surface. The key to confirming the presence of a saltwater ocean came from observing Ganymede's aurorae, which would look bright red to a human able to stand on the surface of the moon and gaze up through its thin oxygen atmosphere. But don't get too excited, it's much too thin to support life as we know it.
Auroral phenomena -- think the bright northern lights of the aurora borealis or the aurora australis down south -- are not fully understood, but are linked to magnetic fields interacting with the solar wind. Ganymede is the only moon in the solar system that generates its own magnetic field thanks to its liquid iron core, but it also lies within the magnetic field of massive Jupiter. As Jupiter's magnetic field changes, it affects the aurorae on Ganymede, causing them to "rock back and forth" according to Joachim Saur, a professor for geophysics at the University of Cologne, who presented the news on a NASA teleconference Thursday.
Saur explained that the rocking effect seemed to be dampened by something else. Rather than altering the aurorae six degrees, as models suggested that they should given the electromagnetic fields involved, they only changed by two degrees, leading scientists to conclude that the rocking is inhibited by a salty subsurface ocean.
"This confirms the existence of an ocean and simultaneously rules out the absence of an ocean," he told reporters.
The news comes on the heels of the finding earlier this week that Saturn's moon Enceladus may contain enough warm water to support life. Ganymede will also now be more competitive when it comes to garnering attention among the Jovian moons -- its sibling Europa and its presumed subsurface ocean has long excited space geeks, even working its way into the priority list for future NASA missions.
Looks like NASA may now need to add another moon to its itinerary for that deep-space journey.