Specs
| What | Data |
|---|---|
| Name | Ganymede |
| Class | Galilean moon |
| Parent planet | Jupiter |
| Diameter | 5,268 km (larger than Mercury) |
| Mass | 1.482 × 10²³ kg |
| Distance from Jupiter | 1,070,400 km |
| Orbital period | 7.15 days |
| Rotation period | 7.15 days (tidally locked) |
| Surface gravity | 1.43 m/s² |
| Discovered | 1610 — Galileo Galilei |
Largest Moon in the Solar System
Ganymede is the largest moon in the entire solar system; bigger than the planet Mercury, though less massive because Mercury has a much denser iron core. If Ganymede orbited the Sun instead of Jupiter, it would be classified as a planet in its own right.
Ganymede is also the only moon in the solar system known to have its own magnetic field, generated by a liquid iron core. This creates auroras near its poles, visible to telescopes as ultraviolet glows.
Surface
Ganymede’s surface is split into two distinct types of terrain:
- Dark regions - ancient, heavily cratered terrain, some of the oldest surfaces in the solar system
- Light regions - younger, grooved terrain formed by tectonic activity that stretched and fractured the crust billions of years ago
Hidden Ocean
Like Europa, Ganymede is believed to harbor a saltwater ocean beneath its icy crust, sandwiched between layers of ice at a depth of around 800 km. The Hubble Space Telescope observed subtle rocking in Ganymede’s auroras that is consistent with a subsurface ocean influencing its magnetic field.
Exploration
The ESA’s JUICE (Jupiter Icy Moons Explorer) mission, launched in 2023, will enter orbit around Ganymede in 2034 — the first spacecraft ever to orbit a moon other than Earth’s.