Europa, Jupiter's hidden ocean
The account
Beneath Europa's ice, creatures were thought to live in a dark sea, far from sunlight.
What investigators found
There is strong evidence of a salty ocean under the ice, but there is still no evidence of life there.
The story
When the Voyager probes flew past Jupiter in 1979, they showed that the moon Europa had a bright, smooth ice surface crisscrossed by cracks, with very few craters. It was the sign of a young crust, renewed by something from below. Years later, magnetic measurements from the Galileo probe indicated that beneath the ice there is, most likely, a global ocean of salt water.
That ocean would be heated by the tidal effect of Jupiter's enormous gravity, which stretches and squeezes the moon. Liquid water, energy and chemistry are exactly the ingredients scientists look for when they think about life. That is why Europa became one of the most promising targets in the Solar System. The Europa Clipper probe, launched by NASA in 2024, will investigate whether this hidden sea could harbor organisms.