One solar day lasts two Mercury years — sunrise to sunrise takes half a year of Earth time.
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. Mercury scores 41.9 out of 100, on 80% 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.
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.
Nobody has ever measured long-term human health at any gravity between 0 and 1 g. Below about 0.1 g, anchoring anything — including yourself — becomes the design driver.
Two orbiters, three flybys, zero landings. Nothing built by humans has ever touched Mercury.
Unprotected survival: Seconds. Vacuum plus a 600 °C swing between sunlight and shadow.
Water ice in permanently shadowed polar craters — Arecibo radar 1992, confirmed by MESSENGER neutron spectroscopy 2012.
The IAU has approved 606 names on Mercury, 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.
