I'm working on a story where the characters are stranded on a planet that turns so incredibly slow that it acts like a tidally locked planet, with one side burning and the other frozen. However because the planet still turns, the characters are forced to out-walk it constantly in the habitable strip, chasing the sun. I can't find anything on the internet that even mentions something like this, so I was wondering if a place with this environment is possible.

  • $\begingroup$ Hi Carxon, welcome to Worldbuilding! If you have a moment, please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods, and how we do things here. $\endgroup$
    – Dubukay
    Aug 27, 2018 at 4:14
  • 9
    $\begingroup$ Are you okay with this near-tidal-locking being a temporary state, or is it something that needs to happen on the timescale of millions of years? It seems like the normal tidal-locking process will include a stage when it's almost locked but not quite, and your adventurers have simply happened to stumble upon it in that stage? $\endgroup$
    – Dubukay
    Aug 27, 2018 at 4:15
  • $\begingroup$ Something like this is written about in Saturn's Children by Charles Stross: "To avoid the extremes of temperature, the city of Cinnabar rolls steadily around the equator of Mercury on rails, chasing the fiery dawn. Thermocouples on the rails drain the heat of daylight into the chill of the wintry night, extracting power to propel the city at a fast walking pace, year in and year out." $\endgroup$ Aug 27, 2018 at 12:51
  • $\begingroup$ Lawrence Watt-Evan's book Nightside City is a detective noir set on a planet which is on its final rotation. $\endgroup$
    – Kenster
    Aug 27, 2018 at 13:31

1 Answer 1


Yes! In fact, we can find it right in our solar system.

Mercury is the closest thing to what you would want. It is in a 3:2 spin-orbit resonance, meaning 3 Mercurian days happen every two Mercurian years. Since it has no atmosphere, there is very little heat distribution going on at the surface, so the day side is scorching and the night side is freezing.

Another example of a planet with very long days is Venus, though it does not have a spin-orbit resonance, the atmosphere does distribute solar heat, and all of the surface is a scorching wasteland, not just the day side.

In conclusion, your planet needs to have

  • No real atmosphere

  • Reasonable distance to the sun (so it can actually be hot enough to be deadly)

  • Very long days

  • 4
    $\begingroup$ Even with an Earth-like atmosphere, there would be enough contrast between day- and night-side to motivate the nomadic movement. Only a super-dense atmosphere like Venus' or Titan's (not to speak of gas/ice giants) would make direct sunlight a secondary concern. $\endgroup$ Aug 27, 2018 at 10:46
  • $\begingroup$ @leftaroundabout I don't think the temperature differential would be great enough to render both day and night sides uninhabitable without making the twilight survivable as well. $\endgroup$ Aug 27, 2018 at 19:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .