Jupiter's Gravity Is Keeping an Alien Ocean Liquid — And It's Bigger Than All of Earth's Seas

A Hidden Ocean Hiding in Plain Sight

There is a world in our solar system that holds more liquid water than every ocean on Earth combined. It isn't a planet. It isn't even particularly large. Europa is about 3,100 kilometers across — roughly 90 percent the diameter of our Moon and only about a quarter the diameter of Earth. And yet, locked beneath its frozen crust lies one of the most extraordinary bodies of water ever discovered.

NASA's comparison of the two ocean worlds gives Earth's oceans an average depth of about four kilometers and a volume of roughly 1.4 billion cubic kilometers. Europa's suspected ocean may average about 100 kilometers deep and contain around three billion cubic kilometers of water. To put that another way: Earth's Mariana Trench, the deepest point in our oceans, only reaches about 7 miles down — Europa's ocean dwarfs it many times over.

The Cosmic Engine Keeping It Warm

At Europa's distance from the Sun, there is almost no solar warmth to speak of. Its surface is a frozen wasteland with temperatures averaging -160°C. By all rights, any water there should be locked solid. The reason it isn't comes down to one of the most elegant mechanisms in the solar system: tidal heating.

Europa travels around Jupiter on a slightly eccentric orbit, so its distance from the giant planet changes. Jupiter therefore tugs on the moon with varying strength during every 3.5-day orbit. The near side of Europa also feels a stronger attraction than the far side. Together, these differences stretch and relax the moon. The repeated deformation is called tidal flexing. Friction within the ice and deeper interior converts some of that mechanical energy into heat, much as repeatedly bending a piece of material can warm it.

But here's the twist: this process would normally burn itself out. Normally, these forces would circularize Europa's orbit over time, shutting down the heat source. However, Europa is caught in a gravitational dance called orbital resonance with two neighboring moons, Io and Ganymede. For every single orbit Ganymede completes, Europa completes two, and Io completes four. Jupiter supplies the enormous gravitational pull, while those two other moons keep Europa from settling into a neat, circular orbit that would eventually turn much of its tidal heater down. Europa's ocean may survive because three moons are caught in a rhythm they cannot escape.

The Big Question: Could Something Be Living Down There?

Beyond Earth, Europa is considered one of the most promising currently habitable environments in our solar system. The ocean is thought to be saltwater, sitting atop a rocky seafloor, with the basic chemical ingredients that life as we know it requires. But recent research has introduced some caution. New calculations suggest its seafloor may be calm, cold, and largely inactive, with little energy to support living organisms. Unlike Jupiter's volcanic moon Io, Europa experiences weaker tidal forces that fail to drive underwater geology.

Still, the debate is far from settled. Other studies have hinted at potential habitability, including in lakes within the icy shell above the ocean. Scientists have hoped that water from this deep ocean might rise through cracks and form shallow reservoirs that future spacecraft could more easily study. The surface of Europa is also geologically young, suggesting ongoing activity beneath the ice.

A Spacecraft Already on Its Way

NASA's Europa Clipper launched on October 14, 2024, on a journey to explore Europa, Jupiter's ocean world. Europa Clipper is not a life detection mission — its main science goal is to determine whether there are places below Europa's surface that could support life. The spacecraft will travel 1.8 billion miles to reach Jupiter in April 2030, where it will orbit the planet and conduct 49 close flybys of Europa.

The mission carries more than instruments. A tantalum metal plate aboard the spacecraft is engraved with a poem by U.S. Poet Laureate Ada Limón, along with a recording of the word "water" spoken in 103 different languages — an artistic element connecting human curiosity with the scientific search for habitability. When Europa Clipper finally reaches its destination, it may answer one of the oldest questions humanity has ever asked — and it will find the answer not by looking toward the Sun, but deep into the dark, gravitationally-squeezed heart of a moon most people have never heard of.