Spinning that fast, Jupiter’s deep, cloud-topped atmosphere is swirled into bands and ribbons of multihued clouds: pale yellow, saffron orange, white, tawny yellow-brown, dark brown, bluish, pink and red. Titanic winds push the clouds across the face of Jupiter at hundreds of kilometers per hour. What lies beneath them? For a century planetary astronomers had cautiously sent probes into the Jovian atmosphere. They barely penetrated the cloud tops before being crushed by overwhelming pressure.

But the inquisitive scientists from Earth persisted and gradually learned that some fifty thousand kilometers beneath those clouds—nearly four times Earth’s diameter—lies that boundless ocean, an ocean almost eleven times wider than Earth and some five thousand kilometers deep. Heavily laced with ammonia and sulfur compounds, highly acidic, it is still an ocean of water. Everywhere in the solar system, where there is liquid water, life exists.

They also found that organic compounds form naturally in the clouds and precipitate down into the sea: particles constantly wafting into the restless ocean, like manna falling from heaven.

Eventually the scientists found that life exists in Jupiter’s boundless ocean, as well. Enormous creatures, as big as cities, cruise through those raging currents as easily as a lad poling a raft along a quiet stream on Earth, feeding themselves on the organics constantly drifting down from above. Lords of their world, these creatures exist where humans and their most inventive technology can barely penetrate.

The humans called them leviathans. And they wondered: Could these beasts be intelligent?