Measured by RAD on Curiosity. A 500-day surface stay plus the round trip is roughly 1 Sv — near the career limit NASA sets for an astronaut.
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. Mars scores 26.6 out of 100, on 100% coverage of the axes. The single worst axis here is pressure (6.4 mbar); the one that most sets Mars 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.
Ten successful soft landings by three agencies. Every one of them arrived with no way home.
Unprotected survival: About two minutes. At 6 mbar your saliva boils before you suffocate.
Polar caps, buried glaciers at mid-latitudes, and ice within a metre of the surface across a third of the planet (Mars Odyssey neutron spectrometer, SHARAD radar).
The IAU has approved 2,049 names on Mars, 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.
