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A Moon That Could Change Everything
Of all the places in our solar system where life might exist beyond Earth, one location keeps rising to the top of scientists’ lists. It’s not Mars. It’s not the clouds of Venus. It’s a frozen moon orbiting Jupiter, about 628 million kilometers from the Sun — a place where sunlight is 25 times weaker than it is here.
Europa is slightly smaller than our own Moon. Its surface is a cracked, reddish-brown expanse of ice. From the outside, it looks desolate and deeply hostile to life.
But beneath that icy crust, something extraordinary may be happening.
What’s Under the Ice
The evidence for a liquid ocean beneath Europa’s surface has been accumulating since the Voyager spacecraft flew past Jupiter in 1979. (You can read more about that historic mission in our Voyager retrospective.) Those early images showed a surface crisscrossed with long, dark lines — cracks that scientists now believe are caused by the constant flexing of the ice shell.
Europa orbits Jupiter in a gravitational tug-of-war. Jupiter is enormous; its gravity is immense. As Europa orbits, Jupiter’s gravity stretches and squeezes the moon slightly — an effect called tidal flexing. This flexing generates heat in Europa’s interior, enough to keep a vast ocean of liquid water from freezing solid.
The Galileo spacecraft, which orbited Jupiter from 1995 to 2003, provided the most compelling evidence. Its magnetometer detected a magnetic field being induced in Europa by Jupiter’s powerful magnetic influence — a signature that is most easily explained by a layer of electrically conductive, salty liquid water below the surface. The measurements suggested an ocean that could be up to 150 kilometers deep.
To put that in perspective: Earth’s deepest ocean point, the Mariana Trench, is about 11 kilometers. Europa’s subsurface ocean may contain more than twice the total volume of liquid water found in all of Earth’s oceans combined.
The Three Ingredients for Life
Astrobiologists — scientists who study the potential for life elsewhere in the universe — generally agree that life as we know it requires three things: liquid water, a source of energy, and the right chemical ingredients (particularly carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur).
Europa appears to have all three.
Liquid Water
We’ve established this one. The evidence for a deep, global ocean is strong enough that most planetary scientists treat it as a near-certainty rather than a hypothesis. Europa almost certainly has liquid water — and lots of it.
Energy
Here things get particularly exciting. On Earth, virtually all life ultimately depends on sunlight as its energy source. Sunlight is far too weak to be useful in Europa’s ocean, where essentially none penetrates through the ice. But in 1977, scientists discovered hydrothermal vents on Earth’s ocean floor — cracks in the seafloor where geothermally heated water rich in minerals gushes out. Thriving ecosystems exist around these vents, completely independent of sunlight, powered entirely by chemical energy.
If Europa has hydrothermal vents — and the tidal heating that keeps its ocean liquid suggests it very well might — those vents could power life in the same way. The seafloor of Europa, pressed against a rocky mantle and heated from within, could be studded with active vents teeming with whatever Europa’s equivalent of microbes might look like.
Chemistry
Europa’s reddish-brown surface markings — those dramatic cracks and streaks — are thought to be salts and organic compounds that have migrated up from the ocean below. The surface is also constantly being bombarded by radiation from Jupiter, which can drive chemical reactions, potentially creating oxidants that might cycle down into the ocean and fuel biological processes.
Scientists have detected water vapor plumes erupting from Europa’s surface — jets of material shooting directly from the ocean into space. If those plumes are confirmed, a spacecraft could potentially fly through them and sample the ocean’s contents without ever needing to land.
What Life on Europa Might Look Like
Let’s be clear: nobody is expecting to find fish. Or anything with more than one cell, for that matter.
The most plausible life on Europa — if it exists — would be microbial. Single-celled organisms, possibly similar to the extremophiles found in Earth’s deep-sea hydrothermal vent communities, living in near-complete darkness under crushing pressure, deriving energy from chemical reactions rather than sunlight.
That sounds modest, but it would be the most significant discovery in the history of science. Finding life anywhere beyond Earth — even a single microbe — would tell us that life is not a fluke limited to our planet. It would suggest that life, given the right conditions, tends to emerge. And in a universe full of ocean worlds, that implication is staggering.
Some scientists have also speculated about life in the ice itself, or even in thin meltwater pockets within the ice shell, where there might be access to both radiation-derived energy from above and heat from below. Life on Earth has proven remarkably creative about finding niches we’d never have predicted.
The Europa Clipper Mission
NASA’s Europa Clipper spacecraft launched in October 2024 and is currently en route to the Jovian system, with arrival expected around 2030. It is one of the most eagerly anticipated planetary science missions of our time.
The Clipper won’t land on Europa. Instead, it will conduct approximately 50 close flybys, swooping through Europa’s tenuous atmosphere and any plumes it encounters, collecting data with nine scientific instruments. Those instruments will measure the composition of the surface and atmosphere, map the surface in high resolution, probe the depth and salinity of the ocean using radar and magnetic measurements, and search for signs of recent or ongoing geological activity.
The Clipper is primarily a reconnaissance mission — it’s designed to tell us where and how a future lander mission should go. But the data it returns will reshape our understanding of Europa and, potentially, of where else in the solar system we should be looking for life.
A follow-on mission — a Europa lander — has been discussed for years. Such a mission would need to survive Europa’s intense radiation environment (the surface receives a punishing dose of radiation from Jupiter’s magnetosphere), drill or melt through the ice, and analyze what it finds in situ. It’s an enormous engineering challenge, but not an impossible one.
Europa in Context: A Solar System Full of Oceans
One of the most remarkable revelations of the space age is how common liquid-water oceans appear to be in our solar system. Enceladus, a moon of Saturn, almost certainly has a subsurface ocean — and its plumes have already been sampled by the Cassini spacecraft, which detected hydrogen, carbon dioxide, and complex organic molecules. Ganymede and Callisto, two other moons of Jupiter, likely have oceans too. Even Pluto may have a subsurface liquid layer.
We live in a solar system apparently full of ocean worlds, and we’ve been focused on Mars — our dry, cold neighbor — for decades. The growing excitement around Europa reflects a broader shift in astrobiology: the recognition that liquid water, not proximity to the Sun, is the key variable.
As we continue pushing the boundaries of human exploration — with missions like Artemis returning humans to the Moon as a stepping stone (read more in our Artemis program overview) — the long-term vision increasingly includes robotic missions to these distant ocean worlds. Europa may be cold, dark, and far away. But it might not be lifeless.
The Bottom Line
Could there be life on Europa? The honest scientific answer is: we don’t know. But the conditions are more favorable than almost anywhere else we know of in the solar system beyond Earth. A global ocean, likely hydrothermal activity, the right chemicals, and billions of years for evolution to do its work.
The Europa Clipper will begin sending back data in the early 2030s. What it finds could be the first chapter of the most profound story ever told.
Further Reading
- Interplanetary by Kevin Peter Hand — Hand is one of NASA’s leading astrobiologists and has spent his career thinking about ocean worlds and the search for life in our solar system. This book makes a compelling, scientifically grounded case for why we may find life beyond Earth within this century — and why Europa is his best bet. Essential reading. Interplanetary by Kevin Peter Hand“>Get it on Amazon
