Is Callisto, Jupiter’s moon with the most craters and third largest in the Solar System, an oceanic world with life?

Dust off your old telescope on a clear night and look up. If you find Jupiter, you’ll likely see four small dots to the side of the gas giant: they are the Galilean moons, four of the 95 natural satellites around the Solar System’s largest planet.

Discovered by Galileo Galilei in 1610, Io, Callisto, Europa and Ganymede are proving to be fascinating topics of study for modern day astronomers.

We’ve already sent a mission to one of them: NASA’s Europa Clipper program was launched back in October of 2024 and is set to perform a number of fly-bys on the moon that is thought to be one huge world of liquid water. The European Space Agency’s JUICE (Jupiter Icy Moons Explorer) mission is also set to take a good look at what’s going on out there.

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In fact, it’s more: NASA believe Europa could well have double the amount of water as we have on Earth. The only problem, if we do find life on Europa, is what to call them... Europeans?

And it doesn’t stop there. Callisto is also thought to have liquid water, too. The small, rocky body is constantly being stretched and compressed by Jupiter’s huge gravitational force, keeping the moon ‘malleable’ like bread dough. Like Europa, the enormous pressure exerted on the moon likely keeps the water moving in tidal formations, increasing the movement of particles and a higher likelihood of interesting things happening under the surface.

Callisto, the outermost of Jupiter’s 95 moons, first caught NASA’s attention back in the 1990s when the Galileo spacecraft detected an unusual response to the planet’s shifting magnetic field.

Since saltwater conducts electricity, scientists theorised that a hidden subsurface ocean might be lurking beneath its icy exterior. While we’re not sure if it does indeed have a moon-wide sea locked beneath a solid ice shell that could be tens to hundreds of miles thick, the recent look into the numbers from 1989 certainly make it appear that way.

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Oh, and Ganymede, Jupiter’s largest moon, appears to have an internal ocean that potentially contains more water than all of Earth’s oceans combined. Aliens, we’re coming for you.

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