I am currently worldbuilding a setting on a hot eyeball world with the habitable zone located around the terminator rim between desert and ice sides.

  • The world is terraformed with terran-descended flora/fauna.
  • Technology is late-Roman period (A.D. 200-350).

Research about tidally locked worlds suggests the main problem for life and civilization would be the hurricane force winds constantly blowing across the planet. I am trying to come up with a way to reduce the winds. I might end up using a handwave (magical nodes that stabilize the weather). But before that, I would like to see if there is a mundane workaround.

One idea I have is a wind-break mountain range ringing large parts of the habitable area (though not all) of the terminator.

What would be the best option for protecting the inhabitants of a tidally-locked world from the weather?

  • $\begingroup$ Can you be specific about the tech level? A target year and Earth location (e.g., 1,000 B.C., China) would be perfect. $\endgroup$
    – JBH
    Oct 28, 2017 at 2:02
  • $\begingroup$ Roughly late imperial roman, I chose that simply because I like the aesthetic of that time period. $\endgroup$ Oct 28, 2017 at 2:17
  • $\begingroup$ Do you require a way for life to evolve on this planet, or merely something to make civilization possible, without the necessity of previous evolution? The second is easier to accomplish, but requires life on the planet to have originated elsewhere, and traveled to the planet in some manner, or conditions having been less harsh in the past. . $\endgroup$
    – Gryphon
    Oct 28, 2017 at 3:02
  • $\begingroup$ @Gryphon, as the OP states in his question, life already exists on the planet with a tech level equivalent to the late Roman Empire era. He's only asking to make civilization possible. $\endgroup$
    – JBH
    Oct 28, 2017 at 3:16
  • $\begingroup$ @JBH, yes I see that. I was merely asking about possible implicit requirements. $\endgroup$
    – Gryphon
    Oct 28, 2017 at 3:20

3 Answers 3


What would be the best option for protecting the inhabitants of a tidally-locked world from the weather?

First, what's the problem with a tidally-locked world? Basically, one side of the planet will always face the system's star. That side would get very hot. The opposite side, being locked in a position of permanent night, is very cold.

Let's not worry about how hot or how cold it is on the respective sides for the moment. The important point is that one of the basic laws of thermodynamics says, I'm paraphrasing here, that heat travels from hot zones to cooler zones. This will happen by whatever conductor(s) is(are) on hand. In this case, the atmosphere will do a great deal of work here. That makes wind. Generally speaking, the hotter the light side is in relation to the dark side, the stronger the wind will be.

So, if you want to kill off those winds or at least slow them down on a planetary level, you have to do something about that temperature differential. If you have technology to terraform the planet then you could also, while you're at it, add a Solar Shield and a Solar Mirror to the mix. I would argue that it may even be easier to do that than try to build reliable protection from the winds on a settlement by settlement basis.

In this case, the Solar Shield I envision is a circular mesh deployed at the L1 point. It would not stop all the light but it would block a percentage of it. The shade lowers the temperature on the light side. Also, a mirror deployed at the L2 point could reflect some light to the dark side. If the makers are smart about it, they would make these two objects complement each other. In other words, the heat energy blocked by the shield on the light side would equal the amount of heat delivered using the mirror on the dark side. Indeed, a step more along that line of reasoning would allow the devices a limited amount of "intelligence" and the ability to give the tidally-locked world real day/night cycles.

So, the version 2 shield is not a mesh but a material that has two states, fully opaque or partly opaque. The control mechanism being how much of an electric current is running through it. This is similar to composite materials used today in high-tech windows of tomorrow. Version 2 of the mirror would likewise be covered with the same material but with a range of fully opaque to clear. That would allow the mirror to go dark as needed. With both devices in place, the light side could experience night while the dark side got day.

Regardless of which versions you use, the end result is to bring the world's areas of extreme down to a more moderate level. That would help with the wind problem. With these great extremes the heat exchange, which is the source of the massive winds, becomes more moderate. That makes the winds more moderate.

Now, I'd like to point out that success here may not cause the wind to cease completely. It is more likely to bring the winds down to a more manageable level. A level that would allow the individual settlements, at a much lower tech level, to build things that could survive the wind.

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    $\begingroup$ It seems like I could incorporate multiple approaches. I can have mountain shielded regions that are fairly tame along with open areas that are windy but not apocalyptic thanks to the heat shields. $\endgroup$ Oct 28, 2017 at 21:19

I've heard that the city of New York has it's own micro-climate which has come about due to the many tall buildings, polution and other factors.

A little digging led me to this article with a quick skim suggesting that many factors can influence micro-climates. Your colonists might have had more success by creating one or two areas with moderate climates through the placement of artificial mountains or hills, tree-breaks, bodies of water and so on before branching out little by little to create new areas as their population grew.

Areas closer to the desert side of things might benefit from a mountain (and some other things - no one solution would be simple), while an area closer to the cold side might have a large forest tract.

Even in a culture similar to the late-Roman era, sophisticated knowledge on this could be easily known/available, as handed down by ancestors and refined over generations, because face it humans adapt their surroundings much better than they adapt to their environment.


Much depends on how much air you have. One of the stable solutions is that all the air freezes out on the dark side, leaving only what is the vapour pressure at the darkside temp. Not much.

With enough air it rises at the sub solar point rushes around, sinks at the dark side, and returns. Depending on how fast this cycle runs you can get anything from constant icy wind to something bearable.

I suspect that the amount of water in the air will also make a huge difference. Water has large latent heat. If you have rivers that flow all the way to the subsolar point, then much of the heat can be transported by water vapour instead of by wind. Since the habitable band is substantially cooler than the sub-solar point I would expect nearly constant rain there, with attendant erosion. If you can even transport half the heat by water vapour it cuts the volume of air moved by a factor of 2, turn hurricanes into mere gales.

A constant cloud layer also moderates the temperatures, reducing the amount of heat that has to be moved.

Another solution would be a pair of planets or a planet and moon tidally locked in orbit around the star.

Or have the planet tidally locked around a brown dwarf or other minimally hot object, and that pair orbits around a more conventional star. The conventional start provides most of the energy. This has a problem of making for longish days

  • $\begingroup$ I was considering having several rivers flowing toward the subsolar point, with one wide enough to be considered a sea by those dwelling on terminator. I like the idea of having the planet locked with a brown dwarf orbiting a star, a bit different than what I was initially thinking but it would let me have a day/night cycle on the nightside. $\endgroup$ Oct 28, 2017 at 21:24

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