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What I'm using your information for:

My planet is small, has a thicker atmosphere than earth and it's orbiting a white dwarf. The main reason I chose it to be a white dwarf is that I read somewhere that these would take much longer to cool than a regular star, because they have a much smaller surface. The reason I need the star for such a long time is, that I want to communicate how unlikely it is that an intelligent alien species similar to ours would evolve. The time between humanity and my alien species should feel like an eternity. At the same time my species is one of many thousand similar ones that lived on that planet one after another. The whole ecosystem stayed roughly the same and just this one species gets replaced every few 100'000 years. -This process should go on for as long as possible.

What I want to know:

The main reason I won't do my research without you is, that I'm really really bad at it: The white dwarf I'm "looking for" should burn its energy as slowly as possible. That's why my planet will orbit quite closely to it, still allowing my ecosystem to exist. It should also have the biggest mass possible and look the same over a long time which (I think) means, that its spectral light will rather be white than blue? -Here's where it ends for me.

  • Does the light of the white dwarf I need look differently from each angle than that of our sun? How?

Edit regarding the comments:

To L.Dutch. Yes, it's tidally locked.

To AlexP. I could imagine that dead ends in evolutionary lines are possible, if the conditions are right. Our way of evolution isn't the only possible anyways. I even wanted to explain parts of it: There's a bacteria-like species that lives in almost every organism. Rumors tell that an intelligent species that lived long ago had developed them to make certain species go extinct for ever. They support the organs of all rather complex species, also their breeding chambers... To your second comment: I never thought about it this way... Species evolving that have comparable sight to us will see their suns color as white anyways. Everything else would depend on the atmosphere and the weather... Thanks.

To Alexander: Exactly.

To Stephen G: I understand what you mean. Why would someone care about the sun, when the main problems are asteroids, the rotation of a planet, the planet cooling down, etc? - There's another bigger planet orbiting the white dwarf blocking/pulling asteroids away. The planet will be heated by the same other planet whenever it comes by, like Titan, just less often. The species aren't like the ones we have on earth. Most of them are able to live for thousands of earth-years and they don't reproduce how "we" do. (would take long to explain) Everything else can be explained by luck or "not talking about it", I guess. The longer the sun stays the same, the more likely it is that there's a very long window where also everything else is in place for the stagnating environment I want my stories to take place in.

to cmm: thanks. Now there's only the "main question" remaining.

to TheDyingOfLight: "universe sandbox" looks really interesting. Thanks for the link.

to Mike Scott: Thanks! Such info was exactly what I was hoping for. Hopefully I'll find a way/an example to explain this...

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    $\begingroup$ How are you coping with tidal locking? If the planet is too close to the star it will end up in an orbital resonance. $\endgroup$ – L.Dutch May 31 at 15:35
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    $\begingroup$ "The whole ecosystem stayed roughly the same and just this one species gets replaced every few 100'000 years": that is not how natural evolution works. Not at all. $\endgroup$ – AlexP May 31 at 15:35
  • $\begingroup$ "Does the light of the white dwarf I need look differently from each angle than that of our sun?" Are there humans on this world? Did the aliens from this world ever visit our solar system? Otherwise, who is to say that it looks different? $\endgroup$ – AlexP May 31 at 15:39
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    $\begingroup$ I don't understand why the estimated 8 billion years before our main sequence Sun (a not untypical period) turns into a red giant is not enough time. It's very unlikely any species currently existing on Earth would be around in any remotely identifiable form in another 4 billion years. Given previous events on Earth, it's quite possible another e.g. eight intelligent species could evolve and die out in that period without overlapping each other. $\endgroup$ – StephenG May 31 at 16:50
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    $\begingroup$ White dwarf stars are highly unlikely to have planets in their habitable zone. Because before a star is a white dwarf, it’s a red giant, and it will engulf any planet that's close enough to the star to be in its habitable zone after it becomes a white dwarf. Your planet would have to have been captured after the red giant phase, which poses other problems. $\endgroup$ – Mike Scott May 31 at 19:17
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How the sky will look depends on the light of the star, the consistency of the atmosphere, and the weather. You have given clues to each of these in your multi-part question.

The starlight will be "white" to any visual system that has evolved in that illumination. We see white light because our experience of "white" is that "white" is the color of natural light from which nothing has been removed. If the sun were cooler, or hotter, the spectrum would change, but eyes which evolved in that spectrum would see it as white.

Your planet's atmosphere is denser than earth. The atmosphere may need a generous quantity of greenhouse gasses. If the star is to last longer than the earth's sun, it would use fuel more slowly, and the emitted energy would be lower. Up to a point the lower stellar output can be compensated for by being closer to the star, but an atmosphere of greenhouse gases helps a lot. You can't be too close to the star or your planet will be ripped apart, so greenhouse gasses may be a friendlier alternative.

The weather is trickier. You say that nothing changes in the ecology, which must mean that mountains aren't growing, the seas aren't changing, and the climate is consistent. I don't know how to do that. Wind and rain cause erosion, which cause change. I think you might need to give up on you "constant ecology", and make something more like earth, with a dynamic balance between growth and destruction with species evolving in competition with others, and species disappearing as they fail to adapt to changes. It would be more likely that your succession of intelligent species could evolve in such a dynamic relative equilibrium that in a world that is completely static.

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  • $\begingroup$ Thanks for all the info. It feels good to have someone invest time into a problem you don't know how to tackle. You've helped a lot better than what I'd deserve to get. -I'm realizing just now how "bad" my three questions were.- I'll explain a few things about my planet to clarify stuff: Most of the species that live on my planet are mother and child at the same time; An egg gets lain, the egg births a child instead of containing one. The child carries its egg-mom. If the child dies, the egg-mom will still be able to create new children. $\endgroup$ – Anton Berkhoff Jun 1 at 22:05
  • $\begingroup$ The egg-mom doesn't need any food or air for the phases in which it doesn't have a child. This way a species can live on for a very long time, even if the conditions aren't ideal.The planet is tidally locked to the white dwarf which means that the climate will roughly stay the same in most areas. Every few thousand years a big planet passes by closely, causing the planet to heat up again and again. That's also how continental plates could/should keep moving for a very long time. Also most of the planets water is contained by a very thick earthlike layer, with root-like life forms living in it. $\endgroup$ – Anton Berkhoff Jun 1 at 22:15
  • $\begingroup$ There is probably more here than can be addressed in comments, which are not meant for extended discussions. I hope to see more questions from you as you develop your world. $\endgroup$ – cmm Jun 2 at 0:26

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