Imagine a world much like Earth, except it is nearly tidally locked to its star, making a complete revolution every few thousand years. The planet is far enough away that there is a band of livable area ~300 hundred miles across. Everything on one side is scorching desert, everything on the other side is ice, and both of these regions are impassable and deadly. I want to avoid vast oceans - let's say no more than 30% of the livable band can be water, and preferably the water is in lakes rather than oceans.

I know that winds are a serious problem for such a planet. It would be very windy and rainy all the time. There would also be no night-time (or true day-time either).

What effect does this have on the flora and fauna of this world? With no night, I imagine we would have no nocturnal hunters. With no seasons, hibernation makes no sense, squirrels won't store nuts away for the winter. But what would replace these, if anything? What sort of animals would thrive?

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    $\begingroup$ Possible duplicate of Consequences of perpetual daytime on plants growth $\endgroup$
    – Mołot
    Dec 7 '16 at 21:30
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    $\begingroup$ Not a duplicate - my question presents a specific planet, and asks about both flora and fauna. The linked question also does not have a well-rated or accepted answer, and those answers do not really answer my question. $\endgroup$
    – SPavel
    Dec 7 '16 at 21:36
  • $\begingroup$ The plants part is a duplicate. The animals part makes it too broad. If this question truly is distinct, perhaps you could edit the question to narrow it down? $\endgroup$
    – kingledion
    Dec 7 '16 at 23:28
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    $\begingroup$ I don't know if this is a handy comment, but a tidally locked planet with a rotational period of a few thousand years would have to be extremely far from the star. Like, nearly Oort cloud, probably too dim to detect optically far. $\endgroup$ Dec 8 '16 at 13:48
  • $\begingroup$ What about a few hundred years? $\endgroup$
    – SPavel
    Dec 8 '16 at 15:35

A paper I found suggests that the sunlit side might not be a burning desert as long as the planet isn't to close to the star.

Basically the difference in heat between the light and dark sides would cause a Hadley cell to wrap around the planet, circulating the heat from the light to the dark constantly (that constant wind you mention), and the increased circulation causes more clouds to build up over the substellar point, which is the point on the planet where the star would be seen directly overhead, and where radiation is most intense. The clouds over the substellar point then create a shield for the ground below as most of the harmful radiation is reflected away.

The high albedo clouds can allow a planet to remain habitable even at levels of radiation that were previously thought to be too high, so that the inner edge of the habitable zone is pushed much closer to the star.

That area would also get a lot of rain because of that cloud cover, and so could avoid the hot eyeball scenario you describe.

Edit: By having the orbit a little closer to the star you'd be able to burn through that cloud cover and push back the ice on the night side more, which would weaken the Hadley cells. You'd still have a lot of rain around the edges of this desert zone, but then the hot eyeball earth would be very likely.

All that aside, life would find its niches, ranging all over the terminator from full light to full dark, and probably even examples of things living in the most extreme areas, especially if the Hadley cells keep hot dry air moving into the darkness and cold wet air moving out into the light.

  • $\begingroup$ I would like the sunlit side to be a burning desert - the premise of the story requires it. $\endgroup$
    – SPavel
    Dec 7 '16 at 19:27
  • $\begingroup$ @SPavel Then having it more on the warm/close side so that the Hadley cells break down a little will probably do the trick. That is mentioned in that paper. And exo-planet weather mostly theory and computer simulation at this point anyway, so why not! I can change my answer to reflect that if you'd like. $\endgroup$
    – AndyD273
    Dec 7 '16 at 19:41
  • $\begingroup$ @SPavel Updated to reflect that information $\endgroup$
    – AndyD273
    Dec 7 '16 at 20:28

What you describe is the Eyeball scenario on a gravitationally locked planet.

The majority of water is stocked in glaciers on the night side, which is all covered with ice, perhaps extending greatly past land as thick ice shelves. Cold air currents may slide ice farther into the twilight zone. There could be arctic mammals and lichens here, particularly if there are thermal springs. Plankton will drift to the night side for animals as long as they are able to access the ocean through the thick ice. Perhaps there are colonies of tenacious mammals continuously maintaining a network of burrows reaching down to the ocean surface.

Water is melting and flowing sunward through the hospitable twilight band. Settlers may have a planetary highway and railway system along the ring. Whether there is temperate climate in the twilight will depend on tectonic activity and mountain placement and how the hot and cool air currents flow. Life may originated underground and emerged from caverns as photosynthesizing plants appeared. Animals could hunt anytime and won't have to migrate seasonally. Larger creatures that live out in the open may have opaque shells in the event of a solar flare, while smaller creepy crawlies seek shelter in the dark side of a mountain. Those who depend on seasons for breeding may not thrive even in the temperate band, but those who make it would have their young seen with them at any given time. There will certainly be a constant food source from vegetation, as flowers will be in bloom at all times and will slowly produce fruit. Trees at the edge of shadow will lean toward the sun, and all flora may look stretched-tall with large, thin leaves that have an extra bitter taste.

The day side is a desert where deeper rivers may flow some distance into the warm but eventually will dry up. Warm wind currents, blowing hot air, will push desert maybe even inside the dark hemisphere. It is likely there is an eternal violent storm in the center of the sunlit desert. Depending on whether the planet's orbit is more elliptical, there will be much more volcanic activity and especially so here. Possibly there could be viscous fiery rivers ever burning and reshaping the landscape.

Hope this is helpful and imaginative.

I largly drew in part from this page, under "Eyeball Planet": http://terraforming.wikia.com/wiki/Tidal_Locked_Planet


In a tidally locked planet, life would adapt. As always, but in a weird way. Your band of life would always in in Twilight, its that type of sunlight where on one side of the sky, its blueish black, while the other would be reddish light of the sun. Since because of the lack of "true" sunlight, plant life would evolve to gain photosynthesis from UV rays, (if I'm not mistaken) which would give the plants a black color instead of green we see everyday. Now, for animal life. I don't know. Most likely, animals would adapt the same, with just that they live on a tidally locked planet. So, they might evolve darker color furs? No clue.

  • $\begingroup$ Why would it have UV rays but not “true” sunlight? Tidal locking and habital zone imply a tiny star m does a red dwarf even give off any UV? $\endgroup$
    – JDługosz
    May 2 '17 at 5:15

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