🌊 Currents of Ganymede's hidden ocean detectable?

A study conducted by researchers from the Institut de Physique du Globe de Paris (IPGP) and the CNRS shows that the convective movements driving the ocean hidden beneath Ganymede's icy surface could generate weak magnetic signals detectable from space.

These signatures could be measured by the European Juice mission, currently en route to Jupiter, opening a new avenue to explore this inaccessible ocean and better understand its dynamics as well as its potential habitability.


Ganymede, the largest moon of Jupiter and the Solar System, hides a vast ocean of salty water beneath a thick layer of ice. For several decades, scientists have suspected its existence, but studying it remains difficult since it is completely inaccessible to direct observations.

In a study published in Geophysical Research Letters, researchers from IPGP and the CNRS show that it would be possible to learn more about this ocean through the weak magnetic disturbances it produces. Their work suggests that the movements stirring Ganymede's deep waters leave a detectable signature from space.

When the ocean leaves a magnetic imprint

Ganymede's ocean is thought to be driven by convective motions related to heat transfer in its interior. These currents move water that is likely rich in dissolved salts, hence electrically conductive.

As this conductive fluid moves through Ganymede's magnetic field, it can generate electrical currents that in turn produce a weak magnetic field. To assess this phenomenon, the researchers combined ocean circulation simulations with magnetic models adapted to the specific conditions of this Jovian moon.

Their results show that the signal produced remains very weak, but it could nonetheless reach a level detectable by current instruments. The signal's intensity depends in particular on the ocean's depth, its salinity, and the speed of the currents flowing through it.

Beyond simply detecting the ocean, these magnetic signatures could also provide information on its internal structure and on how it transports heat.

A target for the Juice mission

These results come as the European Juice mission (Jupiter Icy Moons Explorer), launched in 2023, continues its journey to Jupiter. Once there, the spacecraft will perform several flybys of Ganymede before entering orbit around the moon.

Among the instruments on board is a highly sensitive magnetometer. According to the study's authors, it could be capable of detecting the weak signals produced by the ocean currents simulated in their models.

If this signature is indeed observed, it would offer an unprecedented means of studying an ocean buried beneath hundreds of miles (hundreds of kilometers) of ice. More broadly, this method could be used to explore other ocean worlds in the Solar System, such as Europa or some of Saturn's moons, which are among the most promising environments for the search of conditions favorable to life.