A spacecraft with solar arrays spanning roughly the length of a basketball court is currently crossing the solar system toward one of the most intriguing worlds humans have ever discovered.
Its destination is not Mars.
It is Europa, an ice-covered moon orbiting Jupiter that scientists believe hides an enormous saltwater ocean beneath its frozen surface.
NASA’s Europa Clipper launched on October 14, 2024, and is scheduled to reach Jupiter in April 2030 after travelling about 1.8 billion miles along its gravity-assisted route. Once there, it will orbit Jupiter and make 49 close flybys of Europa.
The mission is often described as part of the search for extraterrestrial life, but there is an important distinction.
Europa Clipper is not designed to detect life directly.
Instead, it will investigate something that may be even more fundamental: whether an ocean beyond Earth has the conditions necessary for life to exist at all.
Europa May Have More Water Than Earth
From the outside, Europa does not look particularly welcoming.
Its surface is an enormous frozen landscape covered with fractures, ridges and reddish-brown streaks. Temperatures are extremely low, and Jupiter’s powerful radiation environment continually bombards the moon.
The interesting part may be hidden underneath.
Evidence collected by previous spacecraft suggests that beneath Europa’s icy shell lies a global ocean of salty liquid water.
NASA estimates that this ocean could contain more than twice as much liquid water as all of Earth’s oceans combined.
That immediately makes Europa interesting to astrobiologists.
Every known form of life on Earth requires liquid water.
Water alone does not guarantee life, of course. A swimming pool contains water, but that does not mean organisms will spontaneously appear inside it.
Scientists generally look for several fundamental ingredients when considering whether an environment might support life: liquid water, suitable chemistry and a usable source of energy.
Europa may possess all three.
Why Scientists Think an Ocean Is Really There
Nobody has drilled through Europa’s ice.
The evidence for its ocean instead comes from several observations.
One of the strongest clues arrived through NASA’s Galileo mission, which explored the Jupiter system between 1995 and 2003.
Europa does not generate a substantial magnetic field of its own. Yet during close encounters, Galileo detected a magnetic response as Jupiter’s enormous magnetic field swept past the moon.
Scientists concluded that an electrically conductive layer probably existed beneath the surface.
A global ocean containing dissolved salts provides a compelling explanation.
Europa’s geology offers additional clues.
Its surface is unusually smooth compared with many other moons, with relatively few enormous mountains or impact basins. Instead, ridges, grooves, chaotic blocks and fractured regions cover much of the landscape.
Some areas look as though enormous pieces of ice have broken apart, shifted and frozen again.
That raises an extraordinary possibility.
Europa may not simply contain an ancient ocean trapped beneath an inactive shell. Its surface and ocean could still interact.
Europa Clipper Won’t Actually Orbit Europa
One might expect a mission dedicated to Europa to enter orbit around the moon.
Europa Clipper will do something different.
It will orbit Jupiter.
From that larger orbit, the spacecraft will repeatedly dive past Europa, gathering observations during 49 close encounters.
The reason is radiation.
Jupiter possesses the strongest planetary magnetic field in the solar system. It traps enormous quantities of charged particles, producing radiation belts capable of damaging spacecraft electronics.
Europa sits directly within this hostile environment.
Remaining close to the moon continuously would expose Europa Clipper to much more radiation.
By following elongated orbits around Jupiter, the spacecraft can spend relatively short periods near Europa collecting data before retreating from the harshest radiation.
NASA has also placed sensitive electronics inside a thick-walled protective vault made from titanium and aluminum.
The spacecraft is effectively being armored against Jupiter.
Nine Instruments Will Examine One Moon Together
Europa Clipper carries nine scientific instruments plus a gravity and radio-science investigation.
They are designed to work together rather than answer isolated questions.
Cameras will photograph Europa’s surface at much higher resolution than previous missions.
Spectrometers will analyze reflected light to identify materials such as ice, salts and potentially organic compounds.
A thermal instrument will search for warmer areas that could indicate recent geological activity.
Other instruments will analyze gases and tiny particles surrounding Europa.
Together, these observations should allow researchers to construct something approaching a three-dimensional understanding of Europa—from the environment surrounding it to the ocean hidden below.
Explore Europa Clipper’s scientific instruments at NASA
One instrument is particularly exciting because it will effectively attempt to look beneath the surface.
NASA Is Sending Radar to Peer Through Europa’s Ice
The instrument is called REASON, short for Radar for Europa Assessment and Sounding: Ocean to Near-surface.
It will transmit radio waves toward Europa’s surface and analyze the returning signals.
Different materials reflect radar energy differently.
By studying those reflections, scientists hope to investigate the structure of the ice shell and potentially identify liquid water within or beneath it. NASA compares the basic concept to creating a kind of CT scan of Europa’s frozen exterior.
This could help answer one of the mission’s biggest questions.
How thick is Europa’s ice?
Estimates have varied considerably, and the answer matters for habitability.
If the shell contains pockets of water or pathways connecting the surface with the deeper ocean, chemicals produced at Europa’s irradiated surface might eventually move downward.
Material from the ocean might also move upward.
That exchange could fundamentally change the chemistry available for potential organisms.
Europa Clipper Will Also “Sniff” the Space Around the Moon
The spacecraft does not necessarily need to penetrate Europa’s ice to learn what lies beneath it.
Europa might bring samples to the spacecraft.
Scientists have investigated evidence suggesting that plumes of water vapor could occasionally erupt from the moon, although the nature and frequency of such activity remain uncertain.
If ocean-related material is being thrown into space, Europa Clipper could potentially fly through or near it.
Its MASPEX mass spectrometer is designed to analyze gases around Europa with extraordinary sensitivity, while the SUDA dust analyzer will examine tiny solid particles.
That creates an enticing possibility.
Material originating from an inaccessible ocean could effectively be delivered into space where a spacecraft can analyze it.
Scientists will be interested in salts, organic molecules and other compounds that help reveal whether Europa’s chemistry could support biology.
But finding organic molecules would not mean NASA had discovered aliens.
Organic chemistry can exist without life.
Context will matter.
The Mission Is Looking for Habitability, Not Aliens
This distinction deserves emphasis because headlines about Europa frequently describe the mission as a hunt for life.
Europa Clipper does not carry instruments specifically designed to announce that extraterrestrial organisms have been discovered.
NASA describes its primary goal as determining whether Europa contains environments capable of supporting life.
The mission will focus on three broad areas: Europa’s interior, composition and geology.
Scientists want to determine how thick the ice shell is.
They want to understand the ocean’s depth and salinity.
They want to identify chemicals on the surface and around the moon.
They want to determine whether material moves between the surface and ocean.
And they want to understand where usable energy might come from.
If those pieces fit together, Europa could emerge as a genuinely habitable world.
That would be an enormous discovery even if Europa Clipper never detects a single organism.
Life on Europa Would Probably Look Nothing Like Science Fiction
If Europa does contain life, scientists are not expecting cities beneath the ice.
Microbial organisms would be a far more plausible possibility.
Europa’s ocean receives essentially no sunlight through kilometers of ice, so photosynthesis like that supporting most ecosystems at Earth’s surface would not be available.
But life does not always need sunlight.
On Earth, ecosystems exist around deep-sea hydrothermal vents where organisms ultimately obtain energy from chemical reactions rather than direct sunlight.
Europa’s ocean may be in contact with a rocky seafloor. If geological processes create chemical energy there, similar principles could theoretically provide an energy source for biology.
NASA identifies this combination of water, chemistry and energy as central to evaluating Europa’s potential habitability.
That possibility has transformed how scientists think about where life might exist.
A habitable world does not necessarily need a warm surface illuminated by a nearby star.
Sometimes the interesting environment may be buried beneath ice.
Europa Could Change the Search for Life Across the Galaxy
This is where the mission becomes much bigger than one Jovian moon.
Ocean worlds appear to be relatively common in the outer solar system.
Saturn’s moon Enceladus also contains a subsurface ocean and ejects material into space.
Other icy moons may contain large reservoirs of liquid water as well.
If Europa turns out to have the necessary chemistry and energy for life, it would strengthen the argument that habitable environments can exist far beyond the traditional “habitable zone” around a star.
That has consequences for astronomy far outside our solar system.
There may be countless frozen moons orbiting giant planets throughout the galaxy.
Their surfaces could look completely lifeless.
Yet oceans could remain warm underneath because of tidal heating and radioactive processes.
The number of potentially habitable environments in the universe could therefore be much larger than a search based only on Earth-like planets suggests.
The Hardest Part Now Is Waiting
Europa Clipper launched in 2024, but Jupiter is extremely far away.
The spacecraft cannot simply point itself toward the planet and accelerate continuously until it arrives.
Instead, its trajectory uses planetary gravity to reshape its orbit and build the energy required to reach the outer solar system.
After years of travel, it is scheduled to enter the Jupiter system in April 2030.
Then the real scientific campaign begins.
Each Europa flyby will add another layer of information.
Radar measurements can be combined with magnetic observations.
Surface images can be compared with thermal maps.
Spectroscopic measurements can reveal the chemistry of regions photographed by the cameras.
Particles collected around Europa can provide another window into its composition.
The result should be the most comprehensive investigation of an ocean world ever attempted.
Europa Clipper Could Answer a Question Humans Have Asked for Centuries
The mission may find that Europa’s ocean is chemically hostile.
Its ice could be extremely thick.
The exchange of useful material between the surface and ocean might be limited.
The necessary energy sources could be insufficient.
Science has to allow those possibilities.
But if the measurements instead reveal a stable salty ocean, active geology, useful chemistry and sufficient energy, the implications will be profound.
NASA will still not be able to say that life exists there.
It will be able to say something almost as provocative:
there is another world in our solar system where life could plausibly survive.
That would immediately strengthen the case for future missions designed to search more directly—perhaps by sampling fresh material from Europa, landing on its surface or, one day, attempting the extraordinarily difficult task of reaching beneath the ice.
Europa Clipper is therefore not racing toward Jupiter to photograph another interesting moon.
It is performing reconnaissance of a hidden ocean.
Earth has oceans filled with life.
Europa appears to have an ocean too.
When NASA’s spacecraft finally arrives in 2030, humanity may begin discovering just how much those two facts have in common.
