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- Ganymede on Wikipedia
Ganymede
Details
Ganymede is Jupiter's largest moon and the largest moon in the Solar System, bigger than Mercury. It is also the only known moon with its own magnetic field, and evidence points to a buried saltwater ocean beneath its icy shell.
Ganymede matters because it refuses to be understood as merely a large moon. It is the largest moon in the Solar System, larger than Mercury, but its size is only the entry point. Around Jupiter, Ganymede behaves like a world with its own internal architecture, surface history, and magnetic environment.
The magnetic field is the feature that makes Ganymede singular among moons. NASA describes it as the only moon known to have its own magnetic field, discovered by the Galileo spacecraft. That field produces auroras near the poles, and Hubble observations of those auroras helped strengthen the evidence for a saltwater ocean buried beneath the ice.
Ganymede also carries a readable surface. Dark, old cratered regions sit beside brighter grooved terrain shaped by tectonic stress, while models point to a layered interior with ice, ocean, rock, and a metallic core. That is why Ganymede matters on this scale: it is not just bigger than expected for a moon, but complex enough to make the category "moon" feel almost too small.
2,298km
Key facts
- Scale fact
- 5,260 kmdiameter
- Estimated age
- ~4.5 billion years
- Composition
- Water ice, silicate rock, metallic iron core and probable saltwater ocean
- Temperature
- ~90-160 K daytime surface
Scale context
Where Ganymede sits on the full axis
Shared physical scale
4,022km
Together, these objects make the size change around Ganymede easy to compare at a glance.
Sources
References for Ganymede
Measurements and descriptive context are compiled by the Scale of Space team from the references below. If you find an error, please let us know.
- Ganymede — Wikipedia
- Visual reference: Wikimedia Commons (NASA / JPL-Caltech / SwRI / MSSS / Kevin M. Gill, CC BY 2.0)
Between the smallest and the largest, perspective is everything.
About
Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.