Ganymede
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.
Surface conditions on Ganymede
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.
What it would take to settle Ganymede
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 55 out of 100, on 100% coverage of the axes. The single worst axis here is pressure (1e-12 bar (vacuum)); the one that most sets Ganymede apart from the other thirteen is radiation.
Below the Armstrong limit (0.062 bar) body fluids boil at body temperature — the difference between needing a mask and needing a pressure vessel. Above 1 bar the problem inverts into containment, and Venus at 92 bar has never let a lander live two hours.
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.
Both directions cost power continuously. A cold world burns reactor output to stay warm; a hot one has no cold sink to dump heat into at all.
Who has been to Ganymede
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 named places on Ganymede
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.
Sources
- Voyager / Galileo SSI / JunoCam — Voyager + Galileo + Juno mosaic, 359 m/px (NASA Trek / USGS Astrogeology)
- IAU / USGS Gazetteer of Planetary Nomenclature
- NASA — Ganymede
- ESA JUICE
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.