In an already exciting time for space watchers, it’s been a particularly exciting week. Only a day after the space community was rocked by new evidence of warm, mineral-rich water on the Saturnian moon Enceladus, NASA claims it has “the best evidence yet” for an underground saltwater ocean on Jupiter’s largest moon Ganymede. The ocean, estimated to be 60 miles thick and containing more water than Earth, is itself buried under a 95-mile thick layer of ice.
The key to the discovery lies in Ganymede’s magnetic field and the aurorae that are produced when protons and electrons interact with gases in high latitude regions, as can be seen in the aurora borealis on Earth. Ganymede is the only moon in our solar system with enough mass to have a magnetic field of its own, and its proximity to Jupiter means that it is also within reach of the massive planet’s magnetic field.
By observing what the NASA press release calls the “rocking motion” of Ganymede’s auroral belts, a team of scientists led by Joachim Saur of the University of Cologne determined that the only thing that could account for the phenomenon was the existence of a saltwater ocean beneath Ganymede’s icy surface:
If a saltwater ocean were present, Jupiter’s magnetic field would create a secondary magnetic field in the ocean that would counter Jupiter’s field. This ‘magnetic friction’ would suppress the rocking of the aurorae. This ocean fights Jupiter’s magnetic field so strongly that it reduces the rocking of the aurorae to 2 degrees, instead of the 6 degrees, if the ocean was not present.
Jupiter’s many moons vary widely in composition and geography, so the finding serves as a further reminder of the importance of locating the “Goldilocks zone” in the search for life beyond our skies. For example, Jupiter’s gravity has turned the relatively smaller and more closely orbiting Io into a hellscape of hundred-mile-long lava flows and volcanoes that blow material hundreds of miles above its surface. The surface of Io is so alive with volcanoes that maps of its surface are difficult to maintain because they can become obsolete the next day.
Unfortunately, anyone thirsting for more information about the tantalizing possibility of life in this massive ocean has a long wait ahead of them. Although the European Space Agency’s JUICE (Jupiter Icy Moons Explorer) mission received a green light to proceed to its next stage of development last November, the mission’s launch is currently scheduled for 2022, and it will take a full eight years to reach Jupiter after that.
(featured image: a map of Ganymede’s surface)