Think of a surface battered by craters. The most bombarded in the Solar System. Now imagine that under that scarred armor lies a vast ocean of salt water: it is Callisto, the moon of Jupiter that is about to rewrite our understanding of ocean worlds.
Yes. Because despite being the most cratered surface in our planetary system, Callisto has kept a secret for decades. In the 90s, the probe Galileo of NASA had captured magnetic measurements that suggested something extraordinary: beneath that icy crust there could be a salty ocean, just like on its “sister” Europe. So why did it take so long for confirmation?
A magnetic 'deception'
The mystery remained unsolved for a long time due to the intense ionosphere of Callisto. Scientists feared that this electrically conductive layer of the upper atmosphere might mimic the magnetic “signature” of a salty ocean. But now, a new in-depth analysis of the data has revealed a surprising truth.
A NASA research team (here the studio) has re-examined with the latest technologies all the magnetic measurements of the eight close flybys of Callisto carried out by Galileo. The use of advanced statistical techniques and computational models has allowed the separation of the ocean signal from that of the ionosphere. The conclusion is clear: only the combined presence of both can explain the observations.
An ocean world on Callisto
The predictions are exciting: Callisto's ocean could be tens of kilometers deep, hidden beneath a crust of ice that could range from tens to hundreds of kilometers thick. Beneath this vast liquid sea, then, lies a rocky core. It's fascinating to think about how much liquid water might exist in our Solar System.
The final confirmation will come soon. The mission Europa Clipper of NASA and the mission JUICE ofEuropean Space Agency, both already launched, will study Callisto closely. The Chinese mission also tianwen-4 could join the exploration of this mysterious world.
A new space for life?
If Callisto is confirmed as an ocean world, it could follow Europa in inspiring research into its potential habitability. The presence of salty liquid water beneath a protective crust of ice opens up fascinating avenues for the search for extraterrestrial life.
The discovery of this hidden ocean on Callisto reminds me of how full of surprises our Solar System still is. Behind the apparent desolation of an ancient, cratered surface lies a dynamic and mysterious world. And perhaps, as we scan the galaxies for life, the answer may lie right here in our cosmic backyard, beneath the craters of a moon we thought we knew.
