Cosmic Scale
Ganymede
Moon of Jupiter · 778 million km from the Sun
How big is Ganymede?
Ganymede is about 5,268 km across.
See Ganymede in 3D, at true scale
Ganymede is the largest moon in the Solar System — bigger than Mercury — and the only one with a magnetic field of its own, generated by a molten iron core. A salty ocean lies deep beneath its ice, holding more water than Earth's oceans.
At a glance
| Diameter | 5,268 km |
|---|---|
| Mass | 1.48 × 10²³ kg |
| Diameter compared with Earth | 0.413 × Earth |
| Orbits | Jupiter, every 7.2 days |
| Ocean | Under ~150 km of ice |
| Discovered | 1610, Galileo |
Good to know
- Its magnetic field carves out a small magnetosphere inside Jupiter's giant one, and drives auroras.
- Europe's JUICE spacecraft, launched in 2023, will settle into orbit around it in 2034 — the first orbit of another planet's moon.
- Dark ancient terrain and bright grooved terrain divide its surface almost in half.