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The story I want to tell is about a world where one side of the planet always is sunlittenand the other side is always drenched in blank. The planet once stopped rotating (tangential meeting with a black hole). That is, it makes one rotation a year.

So, when the planet was still having a day-night rythm, there was a variety of life, comparable to life in Earth. The story deals with the problem how to stay alive in this world. Can this be achieved by simply traveling the planet, so an artificial kind of night and day are achieved? Can people (human-like aliens) survive by going underground? Lets rule out spacetravel as this seems too far-fetched to me.

One problem will be how to keep flora and fauna, necessary for food, alive. One side of the planet will become very hot, while the other becomes extremely cold. Maybe the best place is the transient region between dark and light. There will be a huge temperature gradient there though. Will this cause massive storms.

Animals start to die one by one and the living daylights get dimmer and dimmer. What to do?

Science and technology are advanced. There are hyperfast parallel computers, every means of transport and communication, gene regulation knows no borders, biotech is advanced, even the atmosphere can be manipulated. There is not enough energy though to give the Earth a reboot though.

What can they do? Is all life doomed?

There are animals that can live in the dark. Assuming the animals to be similar to here on Earth (I could have used the Earth I guess...): https://animals.mom.com/animals-that-live-in-dark-cool-places-12573467.html

There are bacteria that can live in the hot, cold, and dark. Mamals will die out soon though.

We have the theory of the eyeball planet, as adviced in the comment below. It shows how such a planet is gonna look like. Mercury is such a planet (like our moon with us, tidally locked with the Sun).

Im not asking if life is possible in a tidally locked planet. The mechanism for the dimished rotation is different and it's pretty clear to me that life on such a planet is difficult, if not impossible. When nothing is done. I'm asking if the alien people can find ways to survive without leaving their home planet. What else can I add?

Deschele Schilder
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Such bodies tend to not be very hospitable to life. The dark side will get extremely cold, the light side extremely hot. If there is an atmosphere this is somewhat alleviated by the heat being dispersed in the boundary zones, but this will result in extremely violent and permanent storms, not ideal either.

You can (and some authors have tried, including Asimov and I think Niven, so you're in good company) envision life existing in deep cracks and canyons in that border zone, shielded from the worst of the winds.

jwenting
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Many astrobiologists believe that such tidally locked worlds would be uninhabitable for beings like humans, or even totally lifeless.

They believe the water would boil on the day side and flow in strong winds to the night side and there freeze solid, never to melt again. And the atomosphere would turn to liquid and then solid on the night side, and so create a wind blowing fromt the day side to the night side and constantly freezing out more and more of the atmosphere.

For example, Stephen H. Dole. in Habitable Planets For Man, 1964, believed that a planet would have to orbit so close to a low mass and low luminosity star that it would become tidally locked by the star's gravity and thus suffer from enternal day on one side and eternal night on the other side. Dole used that to calculate the minimum mass for a star to have a planet habitable for humans.

https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf[1]

Recently, some scientists have claimed that the situation for tidally locked planets might not be as "Dole full" as that.

This pessimism has been tempered by research. Studies by Robert Haberle and Manoj Joshi of NASA's Ames Research Center in California have shown that a planet's atmosphere (assuming it included greenhouse gases CO2 and H2O) need only be 100 millibars (0.10 atm), for the star's heat to be effectively carried to the night side.[83] This is well within the levels required for photosynthesis, though water would still remain frozen on the dark side in some of their models. Martin Heath of Greenwich Community College, has shown that seawater, too, could be effectively circulated without freezing solid if the ocean basins were deep enough to allow free flow beneath the night side's ice cap. Further research—including a consideration of the amount of photosynthetically active radiation—suggested that tidally locked planets in red dwarf systems might at least be habitable for higher plants.[84]

https://en.wikipedia.org/wiki/Planetary_habitability#Red_dwarf_systems[2]

https://web.archive.org/web/20110814012947/http://crack.seismo.unr.edu/ftp/pub/gillett/joshi.pdf[3]

http://www.as.utexas.edu/astronomy/education/spring02/scalo/heath.pdf[4]

And no doubt there are other discussions of factors affecting the hypothetical habitabilty of tidally locked planets.

M. A. Golding
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