Solar System Simulator · Close-up · Jupiter
Jupiter's moons
Jupiter has more than 90 moons, but four big ones hold almost all the mass. Watch them orbit at their real distances and count the laps yourself.
The four big ones
| Moon | Width | From Jupiter | One orbit |
|---|---|---|---|
| Io | 3,644 km | 422,000 km | 1.77 days |
| Europa | 3,122 km | 671,000 km | 3.55 days |
| Ganymede | 5,268 km | 1,070,000 km | 7.15 days |
| Callisto | 4,820 km | 1,883,000 km | 16.69 days |
Galileo spotted all four in 1610. Io is covered in volcanoes, Europa hides an ocean under its ice, Ganymede is the biggest moon in the Solar System, and Callisto is one of the most cratered.
A 1 : 2 : 4 rhythm
Io laps Jupiter four times while Europa laps twice and Ganymede once. Their pulls on each other keep that rhythm locked, and because of it the three can never all line up on the same side of Jupiter.
Nothing in the simulator is scripted. The moons start at their real distances and gravity does the rest: over ten simulated years the rhythm holds, swinging a little but never breaking.
What the simulator does
- The four moons orbit at their real distances, pulling on Jupiter and on each other.
- A counter tallies the laps. Watch Io reach 4 as Ganymede reaches 1.
- Moons disappear behind Jupiter and go dark in its shadow. Drag to tilt, scroll to zoom, tap a moon for a short note.
Questions people ask
How many moons does Jupiter have?
More than 90 known, and more small ones keep being found. The four big Galilean moons hold almost all of the mass.
What is Jupiter's biggest moon?
Ganymede, 5,268 km across. It is the largest moon in the Solar System and wider than the planet Mercury.
Can you see Jupiter's moons from Earth?
Yes. Steady binoculars show up to four points of light in a line beside Jupiter, and they change places from night to night.
Keep going
Every number on this page comes from the simulator's own physics or the real mission record it is checked against. Where the simulation and reality differ, the page says so.