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50 free Europa (Moon) trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Europa is the smallest of Jupiter's four Galilean moons and the most tantalising: a billiard-ball-smooth ball of ice, slightly smaller than our Moon, with a salty ocean beneath its crust that may hold more water than all of Earth's seas. Tidal kneading from Jupiter keeps that ocean liquid, which is why NASA's Europa Clipper and ESA's Juice are on their way. These 50 questions cover the discovery by Galileo (and maybe Simon Marius), the Zeus-lover naming scheme, the 3.55-day orbit, the 100 km water layer and thick-ice debate, lineae, lenticulae and Conamara Chaos, the magnesium-sulfate streaks, the Hubble plume, the brutal radiation dose, and the missions from Pioneer and Voyager through Galileo, Juno, Juice and Clipper's poem-bearing plate. Easy questions stick to the basics; the expert tier asks about albedo, eccentricity and flyby distances. Every answer is cited to a page we checked, with a short explanation so you learn something even when you miss.
30 of 50 questions with answers and explanations. Play the quiz
Q 01What is Europa's surface mostly made of?
Water ice
Gerard Kuiper's ground-based observations confirmed the water-ice composition in 1957.
Q 02What is thought to lie beneath Europa's icy crust?
A liquid water ocean
Tidal flexing keeps it liquid, and it may hold two or three times the water of Earth's oceans.
Q 03Who discovered Europa in January 1610?
Galileo Galilei
He first saw Io and Europa as a single blur on 7 January and separated them the next night.
Q 04Among Jupiter's four Galilean moons, Europa is which?
The smallest
It is also the least massive, yet still a planetary-mass moon visible with binoculars.
Q 05Europa is slightly smaller than which body?
The Moon
At just over 3,100 km across it is the sixth-largest moon in the Solar System.
Q 06Like all the Galilean satellites, Europa is named after what kind of figure?
A lover of Zeus
Europa was the Phoenician daughter of the king of Tyre and became queen of Crete.
Q 07Lacking mountains and craters, Europa is the what known solid object in the Solar System?
Smoothest
Its surface is young because it is so tectonically active.
Q 08What keeps Europa's subsurface ocean liquid?
Tidal heating
Jupiter's pull stretches and relaxes the moon as its slightly eccentric orbit brings it nearer and farther.
Q 09Europa's very thin atmosphere is composed mainly of which gas?
Oxygen
It is produced non-biologically when radiation splits surface water ice.
Q 10In which year was Europa discovered?
1610
Galileo used a 20× refracting telescope at the University of Padua.
Q 11Which Saturnian moon is the only other one known to show water-vapour plumes?
Enceladus
Europa's plumes, if real, erupt at about 7000 kg/s against Enceladus's 200 kg/s.
Q 12Which rocket launched NASA's Europa Clipper in October 2024?
Falcon Heavy
It is the largest interplanetary spacecraft NASA has ever launched.
Q 13Who launched the Jupiter Icy Moons Explorer (Juice) in April 2023?
The European Space Agency
It will make two Europa flybys but is mainly a Ganymede mission.
The Galileo probe orbited Jupiter from 1995 until which year?
Q 21Which observatory imaged a possible 200 km-high plume near Europa's south pole in 2012?
Hubble
More than 20 times the height of Everest, if the interpretation holds.
Q 22Which probes made the first flybys of Europa, in 1973 and 1974?
Pioneer 10 and 11
Their photos were low-resolution compared with later missions.
Q 23In which year did the two Voyager probes pass through the Jovian system?
1979
Their images first hinted at a liquid ocean under the ice.
Q 24Which orbiter made a close flyby of Europa in September 2022?
2003
It was deliberately destroyed in Jupiter's atmosphere to avoid contaminating the moons.
Q 15In myth, Europa was courted by Zeus and became queen of where?
Crete
She was the mother of King Minos.
Q 16How long does Europa take to orbit Jupiter?
3.55 days
Its orbit is nearly circular, with an eccentricity of only 0.009.
Q 17What is Europa's approximate diameter?
3,100 km
That makes it the fifteenth-largest object in the Solar System.
Q 18How does the volume of Europa's ocean compare with Earth's oceans?
Two to three times larger
Estimates put the ocean around 100 km deep under 10–30 km of ice.
Q 19What are the dark streaks crisscrossing Europa's surface called?
Lineae
The larger bands are more than 20 km wide with a lighter central stripe.
Q 20Spectra suggest Europa's reddish streaks may be rich in which salt?
Magnesium sulfate
Sulfur compounds are suspected of supplying the reddish colour itself.
Juno
New Horizons had imaged Europa in 2007 on its way to Pluto.
Q 25Under Galileo's numbering scheme, Europa is Jupiter's satellite number what?
II
Later discoveries of inner moons mean it is now physically the sixth satellite out.
Q 26At its 2024 launch, Europa Clipper was scheduled to enter Jupiter orbit in which year?
2030
Flybys of Europa were planned to begin in March 2031 after gravity assists from Mars and Earth.
Q 27The 2024 NASA Europa mission's name references what?
19th-century clipper ships
The fast merchant ships plied trade routes; the probe will pass Europa as often as every two weeks.
Q 28Europa's surface gravity is roughly what fraction of Earth's?
13%
Too weak to hold an atmosphere thick enough for wind, clouds or a sky colour.
Q 29Which Space Shuttle carried the Galileo probe into Earth orbit in 1989?
Atlantis
Galileo then used Venus and Earth flybys to reach Jupiter in December 1995.
Q 30What icy spikes, up to 15 m tall, may cover Europa's equator?
Penitentes
Overhead sunlight sublimates the ice into vertical blades; they would complicate any landing.