If the polar cap of a tidally locked planet was all ocean, what weather patterns would emerge? The ocean couldn’t be half frozen/half boiling, right? I need a weather pattern so the planet isn’t just a sun blasted desert on the bright side and a frozen wasteland on the dark side. If one (or both) of the poles is an ocean that covers the light and dark sides, could the temperature differentials of the water create wind and other weather patterns?

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    $\begingroup$ What's your single specific question with definite parameters which has an identifiable best answer? $\endgroup$ – Rottweiler on market-day. Sep 16 '19 at 22:58
  • $\begingroup$ Ok, I’m tampering with the idea of a tidally locked planet. I need a weather pattern to cool the sun-facing side so the planet isn’t just blasted desert on one side and frozen wasteland on the other. If the pole is an ocean that covers portions of the light and dark sides, could those temperature differentials create winds and varying weather patterns? $\endgroup$ – Csraves Sep 16 '19 at 23:18
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    $\begingroup$ Tidally locked planets don't have polar ice caps. The poles are indistinguishable from any other point around the planet's terminator in terms of insolation/climate. It will likely have an antistellar ice cap however. $\endgroup$ – Arkenstein XII Sep 16 '19 at 23:27
  • $\begingroup$ @ArkensteinXII is an antistellar ice cap located on the “equator” on the cold side? $\endgroup$ – Csraves Sep 17 '19 at 0:15
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    $\begingroup$ @ArkensteinXII I’m postulating an assumption that a large body of water shared between the light and dark sides will be able to moderate slightly, allow some vegetation and normal weather patterns. I’m just asking if the presence of that ocean allows me to normalize the climate slightly while maintaining scientific accuracy of the situation $\endgroup$ – Csraves Sep 17 '19 at 1:05

The easiest way I can think of to explain a tidally-locked planet without extreme differences in temperature between the day and night sides would be through the structure and density of its atmosphere. Let me explain:

The atmosphere of a planet can have many different effects on a planet's temperature: highly dense atmospheres can have a runaway greenhouse effect that warms the planet considerably; the atmosphere also has the benefit of creating winds that can circulate temperatures between the hotter and colder halves of the planet.

But there is one bottom line: The side facing the sun will be hot, and the side facing away from the sun will be cold. You can't really avoid this fact, because one side is being constantly heated and the other side is getting barely any heat at all. You could have a dense atmosphere, but that will simply make it so that the near side is scorching and unlivable and the far side is simply "less cold."

"Strong constant heating of a planet on one side can change or even control how much weathering occurs on the planet, which can lead to significant and even unstable climate changes. These dramatic climate effects could make a planet that otherwise has the potential for life to instead be uninhabitable."

If you want to have a livable tidally-locked planet, you could:
- 1) have one with a thin Earth-like atmosphere, where there is a habitable zone on and near the border of the light and dark side. However, this would mean the sun is always very low in the sky and near the horizon in those locations, like a constant state of sunset. To these people, completely blue skies would be bizarre and foreign.
- 2) have people living underground on the hotter side or create complicated man-made systems that isolate people from extreme temperature (for example, a giant structured dome)
- 3) give the planet a certain degree of libration. This means that although it is always facing the sun, it would "wobble" back and forth, giving a greater range of variation in temperature and potentially increasing the areas of livability.

You can also read this paper for more helpful information on a tidally-locked planet.


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