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I want to create a tidally locked world with a habitable (broadly Earth like atmosphere and biome that humans could breathe and live in) band stretching around the terminator pole to pole. There would then be a hot hemisphere sunward and a cold hemisphere on the dark side.

I would like to give this world an extreme temperature gradient from the hot side to the cold side to enable the inhabitants to slowly explore further and further into each hemisphere as their technology advances.

So how extreme can the temperature difference be before the habitable band becomes uninhabitable and what ultimately causes it to become uninhabitable?

Bonus I would like to have some liquid water in the habitable zone and liquid oxygen/nitrogen pools and or solid CO2 ice on the dark side but I am warry that if conditions were such that they could form they might accumulate out of control and consume the atmosphere. How can this be prevented?

This question is similar to this one: How extensive could a habitable twilight zone be on a tidally locked planet? except I am looking to see how to maximise the temperature difference whilst maintaining habitability and the mechanisms that could help achieve this.

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  • $\begingroup$ One way to maximize the temperature difference would be thinning the atmosphere and reducing the amount of surface covered in water. Without these fluids to regulate temperature, you would approach something like the moon - with one super-hot side, one super-cold side, and nothing in between. The question is, just how much can you thin the air and water while maintaining habitability? $\endgroup$
    – Zxyrra
    Jan 24, 2020 at 15:04
  • $\begingroup$ I don't have the science to offer this as an answer, but couldn't the habitable zone be in valley which rings the world from pole to pole to pole. If it was an extremely deep valley with gently sloping sides, the atmosphere would be thickest at the bottom, thinning out as one climbs towards either pole. The poles themselves could each have such thin atmospheres that each is practically in vacuum. The sunward pole would be exposed to direct unfiltered sunlight while the opposite pole is exposed to darkest empty space. This might be a stable environment, not doomed to become uninhabitable. $\endgroup$
    – Henry Taylor
    Jan 24, 2020 at 15:43
  • $\begingroup$ Do you want the maximum temperature difference in that world, or in the habitable zone of that world? $\endgroup$
    – L.Dutch ♦
    Jan 24, 2020 at 16:47
  • $\begingroup$ I want the maximum temperature difference between the hot side and the cold side whilst still allowing habitation. Idealy with a graduated change in temerature so thye can explore further as their technology improves. $\endgroup$
    – Slarty
    Jan 24, 2020 at 17:23
  • $\begingroup$ Thermal differences will be smoothed out due to the presence of an atmosphere and oceans. Temperature differences drives weather. Expect the weather to be stormy, very stormy. Note atmospheric circulation smooths out the temperatures on Venus. $\endgroup$
    – a4android
    Jan 25, 2020 at 7:44

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My first impression is that your two desires conflict with each other. 1) maximum temperature difference between light/dark sides and 2) gradual temperature change across a side. You may need to decide which is more important.

There can be a temperature gradient, yes, but I'm assuming it would be small enough that you don't get the effect you're looking for.

If you're ok with the gradient being just barely enough to accommodate the characteristics you want, maybe you can choose the parameters to be right on the edge of what you need. Want dry ice but not nearby? Say the night side is just a little too warm near terminator and just cold enough far away. It's not a large gradient, but it is just enough so you can have one thing nearby and a separate thing farther away.

There could also be other methods of getting what you want. At the furthest reaches of the light side, maybe there is a mountain range which has a lot of some reflective material, so nearby the mountains there is a spot where the reflected light is collected that is heated even more than the rest of the light side.

Now you have several levels of hot areas:

Near the light/dark terminator it quickly reaches hundreds of degrees. During their industrial revolution people managed to protect themselves from the heat long enough to set up conveyers and pipes which direct hot air back or which take objects out far enough to ignite before bringing them back. Imagine if all you had to do to start a fire was place your wood on a conveyer then crank a shaft to make it go out, catch fire, reverse to make it come back. Or to heat your home all you have to do is use fans to suck in the endless supply of hot air.

On the cold side of this they get free food preservation and air conditioning. Ducts and conveyers again.

Since they are piping in hot and cold air don't stop at the terminator; take it to the opposite side. Use the cold air to help you explore further into the hot area and the other way too.

Now they can go further out and they find lakes of liquid tin and lead. It was already hundreds of degrees nearby, it only needs to get a little hotter for these elements to melt. Though, with the lower air pressure you might have to maintain a better temperature gradient, the melting/boiling points may change.

They'll have to advance quite a bit more to explore the area near the reflective mountains. You can make that area almost as hot as you want. Just say the mountains are arranged in a circle and so much energy is concentrated at the center that you get into areas of liquid copper or iron, or where glass forms.

You can use your idea to get some of what you want, then with a few more creative ideas you can get more of what you're looking for.

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