Europa

Europa hides a deep, salty ocean under its icy shell.

What it is

Icy moon hiding a liquid water ocean under its shell, top target in the search for life.

Moon: Orbits a planet rather than the star. Every kind of thing there is →

Its position moves, so there is no fixed place on a map to point at. The Planetarium works out where it is for your own place and date.

A tiny point right beside its bright planet — steady the telescope and wait.

Europa is slightly smaller than our Moon. In weight, about 1/125th of Earth. Its day: tidally locked; same as its orbital period, 3.55 days.

Its surface: Icy shell hiding a liquid water ocean underneath -- a top target in the search for life.; How we know: The Galileo spacecraft detected a magnetic field around Europa that changes in a way that only makes sense with a layer of salty, electrically conductive liquid water beneath the ice; the icy surface is also cracked in patterns like it's floating on something that shifts. Rung 3 — the shape of the solar system
How it moves: Three and a half days -- Europa laps Jupiter twice while Earth spins once a week.
The machines we sent: NASA's Europa Clipper (launched 2024) is on its way there now.

The numbers

Across	3 122 km
Distance from the planet it orbits	671 034 km
Once round its orbit	3.6 days
One spin	3.6 days
Made of, among other things	water, rock (basalt)

Nobody flew a tape measure out there. Every number on this page was worked out from the ground:

Clear tonight? The Planetarium will show you what is worth a look. Then just go out.