I am currently working on a futuristic sci-fi story and here comes the world building part. I have been doing researches and brainstorming for days, but I feel like I may seek creative opinions from others before going on to next steps.

It would be a future era which humans spent the last bit of resources and left the apocalyptic earth for an exoplanet. The humans settled down for a tidally locked planet - not the best place to colonize, but humans survived anyhow. The humans started in the twilight zone for habitability, faced a lot of troubles and ended up spreading on both sides of the planet. The protagonist was born in many generations after, so humans had already adapted to the environment and had solutions to overcome many problems. (Like immense solar activities, storms, temperature imbalance and insomnia on the day side) The day and night hemispheres were like two huge confronting nations, and most humans had never seen people from the opposite hemisphere they were born.

It is not going to be a hard sci-fi, but I would still love to have a convincing world setting. Humans had the technology level to interstellar travels already, so yes I'm aware technology can be a solution for many, yet I don't think I or anyone would appreciate careless "it's just like that" solutions. Below is my list of concerns:

1) I have read how bad a tidally locked planet can be. To ease the climate extremes between two hemispheres, the planet will be set to have a thick atmosphere with oceans, so heat can be slightly more distributed on both sides. But how much land:water ratio is a big problem to me. The amount of land determines the capacity of the human population, and population may have significant effects on the story. I find this one unexpectedly hard to do research on. Though I can easily find articles about habitability of a tidally locked planet, they mention no (or only a little) geology/climate effects on different models.

2) Because of the temperature difference, the heat flow between two sides creates deadly storms and hurricanes. Is it more realistic if most humans, if not only our protagonist, live in a place surrounded by mountains so most of the wind/storm effect is reduced to a more habitable level in order to sustain a stable living and population growth?

3) To sustain life, apart from the natural solutions to decrease temperature extremes, is it probable to have artificial devices to further equalize temperatures? Well, not exactly equalize, maybe more like humans could still freely go outdoor. So it feels like, for example, a cold winter night in the Scandinavia on the night hemisphere, and just any equatorial countries on the day hemisphere. I'm thinking of an optical device that deflects sunlight and changes its levels by detecting outdoor temperatures, so the temperature of a certain area can be maintained in an acceptable level for outdoor activities. Also I'm not very sure if any devices can be put to increase air/water flow to balance temperature differences (which uses up energy) or instead the heat flow should be made used of for power plants (which creates energy)? Or can they coexist and still be work-effective? Can't think of a way though.

4) Energy is also a key element to the plot. Since humans are separated into two opposing "nations", solutions may be different for energy and they don't share new technology to each other. Quite obviously solar energy is going to be widely used on the day side, like every building, every family. What about the night side? I may need a spare, yet ultimate solution for sustainable energy source for the night side, that the day side didn't have. (can be obtained through technology difference) Our protagonist lived on the day side, so this may not be revealed until later in the story - but it's important. I can't think of anything a bit more convincing than nuclear fusion though.

Oh, and in case you are wondering, though the two hemispheres were confronting each other, they were only "politically" or "diplomatically" enemies. That's why if such devices as temperature balancing existed, both sides needed to work on it and maintain the system at work. Neither side would shut it down to mess with the other because both sides needed it. Until maybe when one side figured out a better solution and decided to shut it down, it then would lead to wars by worst circumstances. In this model either the climate devices or energy sources, or both will lead to conflicts between two sides - that's the idea, and also why I need to be careful in these settings.

Would be appreciated for inputs from anyone, thank you.

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    $\begingroup$ This question consists of multiple concise questions. I recommend splitting up these questions into their own questions in order to prevent this question from being too broad. $\endgroup$
    – Aify
    Commented Apr 30, 2016 at 5:07
  • $\begingroup$ This is way too broad in its current form. You have 9-10 questions in this one post, so I'd recommend splitting them up, as @Aify suggested. $\endgroup$
    – fi12
    Commented May 1, 2016 at 15:09

2 Answers 2


Firstly, I think we should mention that the star should probably be a low mass red dwarf: their lower luminosities mean that some of their habitable zones may well be far enough in that they might have issues with tidal locking affecting potentially habitable planets. To ensure that the planet wouldn't likely be baked out by tidal heating, it would probably need to be a star with at least 30% of the Sun's mass; so I'll pick one with 40% of the Sun's mass, to give some margin of error.

At that mass, one can expect the luminosity to be around 2.3% of the Luminosity of the Sun, thus to receive the same 1366 W/m^2 radiant flux, the planet will need to orbit at around 22 million km. A star with 40% of the Sun's mass would reasonably be expected to tidally lock the Earth or another planet much like it, probably within hundreds of thousands of years, no more than a few million years anyway. Most likely it would probably beat the formation of a continental crust anyway, since the oldest evidence for one on Earth is just under 4 billion years old, making it probably 500 million years after formation that it formed.

It's not all bad news though, since some models indicate an atmosphere of only 100 millibar or 10% of Earth's atmospheric pressure would be sufficient to help transport the heat. An ocean would help even more, but extremes of temperature might be constrained to around 60K, which would limit temperature extremes to somewhere in the -40 to +40C sort of range, depending on the exact average surface temperature of the planet. This could potentially be survivable with technology; in fact, they are not that much worse than extreme Arctic and Desert conditions on Earth.

Winds would be an issue: some parts of the planet would be covered by jet streams since the planet is rotating once every 32 days, ie the orbital period at 22 million km from an 0.4 solar mass body. These jets would tend to organise into bands; sustained surface winds would probably remain below 15 m/s (35 mi/h) in the windiest places on the ground, but the jet streams at altitude would likely be in bands, one in each direction around the planet perhaps at 40 m/s (90 mi/h) or so towards the poles and the equator. These might actually be great for air travel though.

Those bands of 15 m/s stable winds at the surface would be great for energy; they could be filled up with corridors of wind farms, 35 mi/h is convertible by turbines that humans can design with current technology, kit generators up in those jet streams could produce even more power.

Point 3 is interesting. You could potentially build huge heat sinks and radiators, pipelines, heat exchangers etc. The undertaking would be absolutely enormous, though perhaps doable for a civilisation that can transport a viable human population to another star system, especially as such a civilisation would likely have the technology to mine asteroids etc.

Energy use could perhaps be reduced by running the main pipelines along the wind alleys where the strongest longitudinal winds were. That way wind turbines could be fixed to the pipeline to power the pumps mechanically; this is more efficient than first converting the energy to another form like electricity and back. For this to not be counterproductive, would need some clever use of heat exchanges and possibly even active compressors and evaporators, though since the material being transported in the pipeline would need to have a greater thermal energy density per unit mass than the wind did, since you effectively extract the same momentum from the wind as you give to the working fluid plus losses due to inefficiency, friction etc. An active system could probably do this though, as they could generate a significantly higher thermal gradient than ambient.

On the night side, you could also perhaps increase the temperature through geothermal technology, exploiting the tidal heating of the rocks due to the close orbit of the star pump fluids down in to the crust, and pipe that heat up to the surface.

It's an interesting idea but I think perhaps it could be engineered to work.

To try and get some idea of the temperature and climate conditions on this hypothetical planet, I obtained information from the following research article; you might find it helpful to read the full paper:


  • $\begingroup$ Can you please use at least some punctuation in your answer? It is hard to read. $\endgroup$ Commented Apr 30, 2016 at 12:05
  • $\begingroup$ @Hohmannfan I just made a suggested edit to fix that. $\endgroup$ Commented Apr 30, 2016 at 18:41

First, I don't want to be a buzz-killer, but I don't really think you can have life on the daylight side of a tidally locked planet. Tidally locked planets occur very close to the parent star. I mean really, really close.

Temperature on the daylight side can easily approach 200-300 °C and if you have placed a thick atmosphere ... well ... good luck. Also, I don't think any terrestrial planet can sustain a thick atmosphere. Look what happened to Mercury (lost all of its atmosphere due to solar winds). And it isn't even tidally locked yet!

Another issue with such a close-sitting planet is that besides the heat, solar winds (stream of charged particles) would fry any and all electronic devices on the daylight side. If they aren't already roasted already due to fiery temperatures, that is.

This all said, let's get to answering your questions now :)

1- Have a large body of water on the planet, but only on the night side. I would suggest 70% water (deep) and 30% dry land as we have on earth. Have this body of water extend only to the twilight zone as it would quickly evaporate in the daylight side. This body of water would help keep the night side warmer than it would have been if totally dry.

2- Living in the mountains is not enough. Your folks should be living in the cave systems. Tornadoes would be as horrible in mountains as anywhere else. You need to be living in a very strong and closed location. Caves are the first thing that come to mind.

3- No current human technology has even the theoretical potential to be effective on the daylight side of a tidally locked planet and make it less fiery. Forget it. Stars are unbelievably hot and massive and being tidally locked is really really bad and puny humans cannot compete with the overwhelming forces of nature with their toys. The best you can do, is to adapt yourself according to the environment and find suitable locations. Forget about modifying things on the daylight side of a tidally locked planet.

4- On the night side, you are going to get a lot of tornadoes and cyclones. Employ really sturdy and heavy windmills to utilize their energy. These will easily provide more than enough power for all population.

  • 1
    $\begingroup$ This all kinda assumes that we are talking about a medium sized star like our sun or perhaps larger. On the other hand a low mass red dwarf perhaps could have a hab zone far enough in to cause tidal locking without being quite as fiery it would probably still need some heavy duty engineering to live on the day side too perhaps fluid compressors, pumps and massive radiators outside to cool a dome (Think giant city sized refrigerator) perhaps the hot fluid could even be piped night side for a civilisation with the tech to even more a sustainable population at interstellar distances. $\endgroup$
    – MttJocy
    Commented Apr 30, 2016 at 7:33
  • $\begingroup$ The smaller the star, the closer a planet would have to be to get tidally locked to it. For a red dwarf (mass range 0.08 - 0.45 solar masses) the zone for tidal locked would be located very close to the star. Closer than the tidal locking zone of a sun-sized star. The same problems would originate. $\endgroup$ Commented Apr 30, 2016 at 10:43
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    $\begingroup$ Not necessarily you are forgetting that the luminosity decreases much more rapidly than the mass and thus gravitational and tidal forces for instance a red dwarf with 0.5 solar masses has a luminosity of just 3.5% the luminosity of the Sun and thus would have an orbit of 28 million km to have an Earth like 1366 W/m^2 solar constant. The 50% reduction in mass reduces the gravitational and tidal forces by a factor of 2 yes but the 5.3 times closer orbital distance increases it by a factor of 5.3^2 or 28 times greater for a total of 14 times greater gravity. $\endgroup$
    – MttJocy
    Commented Apr 30, 2016 at 12:02
  • $\begingroup$ Red giants an lower mass stars bellow about 0.6 stellar masses which includes all the red dwarfs have at least the inner edge of their habitable zones zones close enough to the host star to be in the likely to be tidally locked category, Earth of course is near the inner edge of the habitable zone so if looking for planets with an Earth like solar constant even the largest red dwarfs fall in this range. See this question it even has a handy chart you can check physics.stackexchange.com/questions/12541/… $\endgroup$
    – MttJocy
    Commented Apr 30, 2016 at 12:22
  • $\begingroup$ Thank you very much for the swift responses. And yes as MttJocy said, the tidal locking target I'm aiming for will be a red giant in the star system. The link is really helpful in imagining the actual world. $\endgroup$
    – Yinnes
    Commented May 3, 2016 at 5:55

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