44 Fun Facts About Europa (Moon)

What powers NASA's Europa Clipper spacecraft on its mission to Jupiter?

Solar panels. Sunlight at Jupiter is about 25 times fainter than at Earth, so the probe carries enormous arrays to gather enough power.

Any life in Europa's ocean might cluster around which seafloor feature, as deep-sea creatures do on Earth?

Hydrothermal vents. No sunlight reaches beneath the ice, so anything living there would have to run on chemical energy, as the communities around Earth's vents do.

Galileo first named Europa and its three sister moons after which powerful family, his patrons?

The Medici. Galileo called the four moons the Medicean Stars to honour his patrons, but the tribute faded and astronomers now call them the Galilean moons after him instead.

Among Jupiter's four Galilean moons, Europa is which?

The smallest. Yet it drew NASA's largest planetary spacecraft: Europa Clipper, launched in 2024 to find out whether this little world could support life.

Europa is slightly smaller than which body?

The Moon. Europa is about 90% as wide, so it would look much the same size in our night sky, yet far brighter, because its icy surface reflects several times more sunlight.

Like all the Galilean satellites, Europa is named after what kind of figure?

A lover of Zeus. In the myth he took the form of a white bull, and when the Phoenician princess Europa climbed on his back he carried her off across the sea.

Its young, shifting ice gives Europa which record among the Solar System's known solid bodies?

Smoothest. Europa has no mountains or tall cliffs, a flatness that suggests its icy crust was once soft and mobile.

What keeps Europa's subsurface ocean liquid?

Tidal heating. Europa's slightly oval orbit carries it nearer to and farther from Jupiter, so the planet's gravity keeps stretching and relaxing it, and that flexing generates heat.

Charged particles splitting Europa's surface ice produce a very thin atmosphere made mainly of which gas?

Oxygen. Charged particles from Jupiter split the frozen water into hydrogen and oxygen; the lighter hydrogen drifts off into space, leaving a wisp of oxygen that no living thing made.

Galileo's 1610 discovery of Europa and its sister moons was strong evidence against which old belief?

Everything orbits the Earth. Here were four bodies plainly circling Jupiter instead, which backed Copernicus's idea that the Earth is not the centre of all motion in the heavens.

Europa's suspected water plumes would echo the proven jets of which moon of Saturn?

Enceladus. NASA's Cassini probe flew straight through its jets and sampled the spray, a trick scientists hope to repeat at Europa if its plumes prove real.

Which rocket launched NASA's Europa Clipper in October 2024?

Falcon Heavy. Congress had ordered NASA to fly the probe on its own Space Launch System, but NASA later won permission to buy a commercial launch instead.

Who launched the Jupiter Icy Moons Explorer (Juice) in April 2023?

The European Space Agency. Juice rode an Ariane 5 from French Guiana and is taking eight years to reach Jupiter, stealing speed from flybys of Earth and Venus on the way.

How did NASA deliberately end the Galileo probe's mission in 2003?

Crashed it into Jupiter. NASA destroyed its own orbiter rather than risk it one day hitting Europa and contaminating the hidden ocean it had helped to reveal.

In Greek myth, the princess Europa was carried across the sea and became queen of where?

Crete. There she became the mother of Minos, the legendary king whose labyrinth was said to hold the Minotaur.

Since Europa always shows Jupiter the same face, how would the planet appear from that side?

Fixed in one spot. Europa turns once on each 3.5-day lap, so from its near side Jupiter would hang in place and never set, while from the far side it could never be seen.

Which technology will Europa Clipper use to peer through the ice shell and gauge its thickness?

Radar. The probe will beam radio waves into the ice and read the echoes, which should show how thick the shell is and whether pockets of water lie inside it.

Europa's hidden ocean is thought to hold about how much water compared with all of Earth's oceans?

About twice as much. Europa is only a quarter as wide as Earth, but its ocean is thought to be 60 to 150 km deep, far deeper than any sea on our planet.

What are the dark streaks crisscrossing Europa's surface called?

Lineae. They look like cracks where the icy crust pulled apart and darker material welled up to fill the gap, much as new seafloor forms along Earth's mid-ocean ridges.

In 2019, scientists found that yellow patches on Europa's surface are which everyday substance?

Table salt. Lab tests showed plain sodium chloride turns yellow under conditions like those on Europa's surface, and finding it there suggests the hidden ocean may be chemically closer to Earth's seas than anyone thought.

Which observatory spotted signs of a possible water plume near Europa's south pole in 2012?

Hubble. It never saw water itself: its spectrograph caught a faint ultraviolet aurora, read as water vapour being torn apart above the pole, and the plumes are still unconfirmed.

Which probes made the first flybys of Jupiter and Europa, in 1973 and 1974?

Pioneer 10 and 11. Pioneer 10 was the first spacecraft to cross the asteroid belt and reach Jupiter, though its photos of Europa were too coarse to show the cracks later probes revealed.

The Voyager probes' 1979 photos showed that Europa has surprisingly few of which surface feature?

Impact craters. Old surfaces are pocked with them, so finding only a handful meant something keeps wiping Europa's face clean, and its surface is now judged to be geologically young.

Which orbiter made a close flyby of Europa in September 2022?

Juno. It raced past about 350 km above the ice with only a two-hour window to gather data, the closest any spacecraft had come to Europa since Galileo in 2000.

Europa Clipper's looping route to Jupiter uses gravity assists from Earth and which other planet?

Mars. The probe skimmed about 880 km above its surface in March 2025 to bend its path, because flying straight to Jupiter would have taken far more propellant.

Fully unfolded in space, Europa Clipper stretches about the length of what?

A basketball court. It will never land: the plan is to swoop past Europa 49 times, on some passes dipping to just 25 km above the ice.

In 2023 the James Webb Space Telescope found which carbon-bearing gas frozen on Europa's surface?

Carbon dioxide. It was concentrated in a patch of young, recently disturbed ice, so scientists think the carbon welled up from the ocean below instead of arriving on meteorites.

Which Space Shuttle, later the last ever to fly, carried the Galileo probe into orbit in 1989?

Atlantis. Its cargo's booster was too weak for a direct flight, so Galileo spent six years borrowing speed from flybys of Venus and Earth before it reached Jupiter.

What is thought to carve the 15-metre blades of ice that may cover Europa's equator?

Direct sunlight. With the Sun overhead, the ice turns straight to vapour and deepens into blades called penitentes, which would make any landing there treacherous.

Galileo publicly accused Simon Marius, a rival astronomer, of what?

Plagiarism. Marius said he saw Jupiter's moons first, but his earliest recorded observation, dated 1609 on the old Julian calendar, fell in January 1610 by Galileo's calendar, a day after Galileo's own.

The Juice probe will fly past Europa twice, but which other moon is it built to orbit?

Ganymede. After months of looping around Jupiter and skimming past its other icy moons, Juice is due to end its tour by settling into orbit around Ganymede itself.

What did the Galileo probe detect around Europa that remains the best evidence for its hidden ocean?

A magnetic disturbance. Jupiter's field was distorted near Europa as if it held a deep layer that conducts electricity, and a global ocean beneath the ice is the likeliest candidate.

The pits and domes freckling Europa's surface suggest that what is slowly rising from below?

Warmer ice. Heat from below seems to make the shell slowly churn: cooler, denser ice sinks while warmer ice wells up, pushing up the domes and spots scientists call lenticulae.

Europa's Conamara Chaos, a jumble of broken ice rafts, is named after a rugged region of which country?

Ireland. Its namesake is Connemara in the country's west; on Europa the region's huge ice blocks appear to have broken loose, drifted and tilted before freezing back into place.

Why are Europa Clipper's electronics sealed inside a thick-walled metal vault?

To block Jupiter's radiation. Europa orbits inside belts of charged particles trapped around the planet, and the vault's titanium and aluminium walls slow the damage they do to the probe's electronics.

Which US Poet Laureate wrote the poem engraved on Europa Clipper?

Ada Limón. NASA commissioned the poem, In Praise of Mystery, and it now rides toward Jupiter engraved in her own handwriting on a metal plate.

NASA's buoyant BRUIE rover is designed to explore an alien ocean by driving where?

Along the underside of the ice. BRUIE floats up against the frozen ceiling and rolls along it on two wheels, a trick engineers have already tested beneath the ice in Antarctica.

Which chemical, sold in pharmacies as a disinfectant, has been detected in Europa's surface ice?

Hydrogen peroxide. It is thought to form as particles streaming from Jupiter batter the frozen water, and if any is carried down to the ocean it could serve as chemical fuel for simple life.

In which 1610 book did Galileo announce his discovery of Europa and Jupiter's other large moons?

The Starry Messenger. Galileo at first took the moons for distant stars, worked out within days that they were circling Jupiter, and had the book in print by March 1610.

Europa Clipper carries a microchip stencilled with more than 2.6 million what?

Names from the public. NASA invited people to sign on to its 'Message in a Bottle', and the chip sits on a plate etched with the word for water as spoken in 103 languages.

A 2022 study found a small twin of Europa's double ridges on which icy part of Earth?

Greenland. Surveys showed the ridge there formed as a pocket of water inside the ice sheet refroze and cracked, hinting that Europa's shell may be dotted with shallow water pockets too.

Which famous equation is etched onto the metal plate that seals Europa Clipper's electronics vault?

The Drake Equation. Frank Drake wrote it in 1961 to estimate how many civilisations might be out there, a fitting passenger on a probe sent to ask whether Europa could support life.

Europa circles Jupiter once for every two orbits made by which inner neighbour?

Io. A third large moon keeps the same beat, and the regular tugs the three give one another stop Europa's orbit from ever settling into a perfect circle.

In 1614 Simon Marius credited which astronomer with suggesting the mythological names of Jupiter's four big moons?

Johannes Kepler. Marius printed the names he proposed, but astronomers ignored them for more than two centuries and stuck with Galileo's plain numerals instead.