Moon of Jupiter

Europa

An icy moon of Jupiter hiding a deep salty ocean beneath its cracked white shell

Key facts

Diameter: About 1,940 miles / 3,120 km (a little smaller than our Moon)
Distance from Jupiter: About 417,000 miles / 671,100 km
One orbit: About 3.5 Earth days
One day (rotation): About 3.5 Earth days, the same as its orbit, so one side always faces Jupiter
Surface temperature: About minus 160 °C at the equator, minus 220 °C at the poles
Discovered: 8 January 1610 by Galileo Galilei
Named after: Europa, a Phoenician princess in Greek mythology
Surface: Smooth water ice with long brown cracks and very few craters
Ice shell: About 9.3 to 15.5 miles / 15 to 25 km thick
Ocean beneath: 37.3 to 93.2 miles / 60 to 150 km deep, more than twice the water in all Earth's oceans
Visited by: Pioneer 10 and 11, Voyager 1 and 2, Galileo, New Horizons, Juno; Europa Clipper arrives 2030, JUICE 2031
Jupiter's known moons: 115 as of August 2026

About Europa

Europa is a moon of Jupiter. It is white and smooth like an egg. It is covered in ice. The ice has long brown cracks. Under the ice there is a big ocean. The ocean is salty and dark. It holds more water than all our seas. Europa is very cold on top. It is warmer down deep. Jupiter squeezes and stretches Europa. That keeps the ocean from freezing. A spaceship called Europa Clipper is on its way. It will look for signs of life. Would you like to swim there?

Europa is the fourth largest of Jupiter's moons and the smoothest. It is a sphere about 3,120 kilometres across, a little smaller than our Moon. Europa orbits Jupiter at a distance of about 671,000 kilometres. One orbit takes about 3.5 days, and Europa rotates once in the same time.

That means the same side always faces Jupiter, just as our Moon faces Earth. The surface is water ice, criss-crossed by long brown cracks called lineae. At the equator the ice is about minus 160 degrees Celsius. Beneath the ice, scientists are confident there is a salty liquid ocean.

NASA thinks the ice shell is about 15 to 25 kilometres thick. The ocean below may be 60 to 150 kilometres deep. It could hold more than twice as much water as all Earth's oceans. Jupiter's gravity stretches and squeezes Europa as it moves along its slightly oval orbit.

This tidal heating keeps the water from freezing solid. Europa has a very thin atmosphere made mostly of oxygen. Galileo Galilei discovered Europa in January 1610, along with three other moons. NASA's Europa Clipper spacecraft left Earth in 2024 and reaches Jupiter in 2030.

It will fly past Europa 49 times to find out whether the ocean could support life.

Europa is the smallest of Jupiter's four Galilean moons and the sixth-closest to the planet. JPL gives its mean radius as 1,560.8 km, so its diameter is about 3,120 km, slightly smaller than Earth's Moon. Its density of 3.01 g/cm³ points to a rocky interior beneath an outer layer of water. Europa orbits Jupiter at a mean distance of about 671,100 km with a period of about 3.5 days, rotating synchronously so one hemisphere always faces the planet. It sits in a 1:2:4 Laplace resonance with Io and Ganymede, which keeps its orbit slightly eccentric (0.009) and drives the tidal flexing that heats its interior.

The surface is water ice with a high albedo and remarkably few craters. NASA estimates the surface is no more than 40 to 90 million years old, meaning it is continually renewed. Long reddish-brown fractures called lineae and jumbled regions known as chaos terrain suggest the shell has broken and refrozen repeatedly. Surface temperatures are around minus 160 °C at the equator and minus 220 °C near the poles. The atmosphere is extremely tenuous and composed mainly of oxygen, produced when Jupiter's radiation splits water molecules in the ice.

NASA's current figures put the ice shell at roughly 15 to 25 km thick, over a salty ocean 60 to 150 km deep holding more than twice the water of all Earth's oceans. The ocean is inferred rather than seen directly: Galileo's magnetometer detected an induced magnetic field best explained by a conductive, salty layer. Hubble observations in 2012 hinted at water plumes rising some 200 km, though these remain unconfirmed.

Europa was discovered by Galileo Galilei on 8 January 1610; Simon Marius claimed an independent discovery and later proposed the mythological names. It is named after a Phoenician princess in Greek myth carried off by Zeus. Pioneer 10 and 11 (1973 and 1974), Voyager 1 and 2 (1979), Galileo (in orbit 1995 to 2003), New Horizons (2007) and Juno (a flyby of about 352 km on 29 September 2022) have all observed it. Galileo was deliberately flown into Jupiter on 21 September 2003 to avoid ever contaminating Europa. NASA's Europa Clipper launched on 14 October 2024 and arrives in April 2030 for 49 close flybys; ESA's JUICE, launched 14 April 2023, reaches Jupiter in July 2031. As of August 2026, Jupiter has 115 known moons.

Did you know?

Europa's ocean is hidden under ice, yet it probably holds more than twice as much water as every ocean on Earth put together.
Europa's surface is so young, no more than about 90 million years old, that it has very few craters compared with most moons.
NASA crashed the Galileo spacecraft into Jupiter on purpose in 2003 so it could never accidentally land on Europa and contaminate it.

Neighbours around Jupiter

Ganymede
Callisto
Io
Amalthea
Himalia
Thebe
Elara
Pasiphae
Carme
Metis

Questions children ask

Is there really an ocean under the ice on Europa?

Scientists are confident there is. The Galileo spacecraft found that Europa bends Jupiter's magnetic field in a way that only a salty, electrically conducting liquid layer can explain. The ocean is thought to be 60 to 150 kilometres deep beneath a shell of ice roughly 15 to 25 kilometres thick.

Why doesn't the ocean freeze when it is so cold?

Europa's orbit is slightly oval, so Jupiter's gravity squeezes and stretches the moon as it goes round. This flexing, called tidal heating, warms the inside of Europa enough to keep water liquid, even though the surface is about minus 160 degrees Celsius.

Could anything live on Europa?

Nobody knows yet. Europa has liquid water, energy from tidal heating, and possibly the chemical ingredients life needs. NASA's Europa Clipper will study the ocean from orbit around Jupiter from 2030. It is looking for the right conditions for life, not for living creatures themselves.

What are the brown lines on Europa?

They are long cracks in the ice called lineae, up to about 20 kilometres wide. As the ice shell shifts, the cracks open and salty water or slush wells up and freezes. Radiation from Jupiter then darkens the salts, giving the lines their reddish-brown colour.

Quick quiz

Three questions for space cadets. Nothing is recorded.

What lies beneath Europa's icy surface?
Who discovered Europa in January 1610?
About how long does Europa take to orbit Jupiter once?

Where next?

The Moon

Enceladus

Ganymede

Written by Anthony (A.Z. Storyworks). Facts checked against NASA Science and JPL, September 2026. Moon counts as of September 2026.

Sources