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Could a planet with one side always facing its star have a temperate zone between the far side and near side that can be suitable for an ecosystem to exist? Here are the conditions:

  1. The planet has an atmosphere similar to Earth and is about the same size as Earth.
  2. The planet has the same total amount of water as earth.
  3. The planet orbits its star at the same pace as the Earth orbits the Sun.
  4. The planet very gradually became tidally locked over billions of years.

The side facing the star would be far too hot to survive in and the said facing away too cold. Could a temperate zone exist between these two sides that can sustain life?

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    $\begingroup$ Exist yes, originate unlikely. $\endgroup$ – Alexander Sep 15 at 16:05
  • $\begingroup$ I thought this "sky abyss" scenario worldbuilding.stackexchange.com/questions/174248/… was a cool way to worldbuild refugia for life on such a planet. $\endgroup$ – Willk Sep 15 at 16:54
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    $\begingroup$ I voted to close this as a duplicate, but it should be noted there were several questions I could have chosen as the duplicate reference (just in case someone thinks the axis of rotation would make a difference in this case). Life on tidally-locked planets has come up a number of times. If you disagree with this vote, please review the search list and explain why none of those questions answer yours. Thanks. $\endgroup$ – JBH Sep 15 at 20:53
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    $\begingroup$ This is a similar (but different) question, that might help with answering this one: worldbuilding.stackexchange.com/questions/358/… $\endgroup$ – cowlinator Sep 16 at 1:48
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    $\begingroup$ @MintySweeTea Similar questions on WB.SE seem to agree that tidal locked worlds are at least theoretically habitable. Starting as a non-locked planet that slowly settled into this state over evolutionary significant time frames only makes life more likely, not less. $\endgroup$ – Nosajimiki Sep 16 at 2:50
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We don't know

So far, the only life that has been discovered is on Earth, and we don't really know specifically are the critical parameters which allowed biogenisis to begin and evolve into complex life. We have lots of theories, but there are a lot of unknown pieces. However, it's certainly possible, and it's your world and your story, so go for it.

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Yes. If this happened to Earth life will just survive.

  • Microbes that currently exist on Earth will be able to survive on the hot side.
  • Deep Ocean (>1km) life will survive planet wide. Normal ocean life will survive in the borders.
  • Humans in bunkers will be able to survive deep underground anywhere, but you'd want your access point near the border zone, on the cold side (hot side would have insane thermals), cold side would just have predictable, strong winds.
  • No plant life that's currently on Earth will survive fully in either the hot or cold side. Some plants and animals will survive on the border zone.

This question is related to, Climate of a No-Axial-Spin Earth?, just without the seasonal variations. I've done some maths in there which almost all applies here. Read that answer for where all the storms will be.

Hot side will be 102 degrees C still, cold side will get much colder than that answer answer. I'm estimating about -170 at sea level (just too warm to see pools of liquid oxygen).

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Atmospheric and oceanic circulatory systems would enable transport of substantial amounts of energy to keep the dark side warmed and the light side cooled to a very significant extent.

The dark side would still become extremely cold and the light side extremely hot by Earth standards but not as extreme as might be imagined. There would be limited life and less ice free water available (the dark side would freeze over) to absorb carbon dioxide. But but with ongoing volcanism still generating carbon dioxide, the atmospheric concentration of carbon dioxide would likely increase creating an enhanced greenhouse effect and warmer air currents.

We don't know for sure how likely it is that bio-genesis will occur on a planet but assuming it did occur as it did on our Earth, bacterial life would spread across the planet before gravitational locking.

Complex life could easily develop in the deep oceans around hydrothermal vents at any time and life in the oceans in general would also be highly likely.

After locking plant life might well evolve in higher latitudes in the more temperate regions between the ice covered terminator and the very hot tropical deserts. And with plant life animal life might also evolve in this area.

During the time before total gravitational locking when the planets rotation was still a different length to it's year, animals and especially marine creatures might be able to migrate and remain in a survivable environment. Annual plants that set seed would also be able to survive extended periods of freezing.

As a partial example of energy transport mechanisms look at the north pole. This spends 6 months of the year in darkness. Although it gets very cold and the sea freezes we do not see cryogenic temperatures because air and water currents such as the gulf stream transport vast quantities of heat energy into the arctic ocean.

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