Ganymede generates a real magnetic field from a liquid iron core, carving a bubble inside Jupiter's — which is why its surface dose is 60 times lower than Europa's.
Every figure below is tagged with where it came from. Measured means an instrument read it on or at the body; modeled means it was computed and never directly observed.
No world off Earth is habitable — the honest habitable fraction of every surface here is zero. What can be answered is how far each one sits from Earth along the seven axes a habitat has to buy its way out of. Ganymede scores 52.1 out of 100, on 100% coverage of the axes.
Below the Armstrong limit (0.062 bar) body fluids boil at body temperature — the difference between needing a mask and needing a pressure vessel.
Shielding is mass, and mass is the single most expensive thing to move. Above roughly 1 mSv/day a surface habitat has to be buried.
Delta-v sets what a launch costs; cruise time sets how much consumable, shielding and crew patience each kilogram of payload drags with it.
Past the asteroid belt solar panels stop being an option and a settlement needs fission, which means importing fuel.
Never landed on. ESA's JUICE arrives in 2031 and will enter orbit around Ganymede in 2034 — the first spacecraft to orbit a moon other than our own.
Unprotected survival: Seconds.
Water-ice crust over a subsurface saltwater ocean, probably sandwiched between ice layers and holding more water than Earth's oceans.
The IAU has approved 196 names on Ganymede, each drawn from a theme the naming committee chose for this world. Every name in the scene above is one of them, placed at its catalogued coordinates.
Imagery is public-domain NASA/USGS mission data, streamed live from NASA Trek as a plate-carrée tile pyramid and draped on our own sphere — no third-party globe library and no cached copy of anyone else's map.
