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I'm trying to create my planet orbiting a red dwarf, honestly I've thought other scenarios but it's like every answer opens new questions. I'll just say what I want my planet to be and I'd like your help(please) to understand how it would work.

I'm new with worldbuilding(started yesterday), so bear with my lack of knowledge, if you don't want to use your time answering, I'd like research sources too.

I want the flora to be mainly black, so the sunlight has to be somewhat weaker, which would make the planet(or the habitable zone) fairly cold.

The planet being tidally locked seems to be the common, and I don't mind, apparently the habitable zone would be the ring around the planet between the parts that do and don't face the star, but I don't know if such a thing is entirely possible, what are the complications the inhabitants of such a planet face?

Apparently it doesn't have to be tidally locked, but I didn't understand how that works, apparently it would have to have some kind of moon orbiting around it?

If you want to show off your knowledge and tell me how the sky would appear...I'll be impressed.

If it needs something unlikely to happen for desired situations I don't mind either, the planet was somewhat "made" by "gods".

Yes, sorry, I don't know much, whoever gives the time to answer, know that I'm grateful.

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    $\begingroup$ Your flora would in all likelihood appear dark blue green (cyan). Because the flora would evolve to absorb red light. A red dwarf is a small star. Your planet would be small. It would be much closer to the star than we are. Think Mercury.. it would therefore have a thinner atmosphere.. with a reddish hue. $\endgroup$
    – Richard
    Commented Dec 28, 2018 at 0:33
  • $\begingroup$ @Richard "Your planet would be small" - why? $\endgroup$
    – Alexander
    Commented Dec 28, 2018 at 0:35
  • $\begingroup$ To be in the habitable zone of a red dwarf it would need to be in close orbit. A large rocky planet in such close orbit seems unlikely... It's not impossible (at least I don't think it is) but my understanding is that it is always smaller planets that orbit closest. $\endgroup$
    – Richard
    Commented Dec 28, 2018 at 0:37
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    $\begingroup$ @Richard You mean like how Mars is bigger than Earth? Seriously it is much more complex than that. As in, it is pretty hard to be provably wrong when deciding your planet size unless you decide to develop and share an absolutely insane amount of useless astronomical data. Just to be clear your thinking is not really wrong, real world star systems are just too complex for it to be a practical issue for most world building. And honestly with a red dwarf star I am not sure if we (as a species) actually know enough to build a fully realistic system with any confidence. $\endgroup$
    – Ville Niemi
    Commented Dec 28, 2018 at 7:10
  • $\begingroup$ @VilleNiemi Heck, even within our own system, there's so much we're still learning. Though to you last point, I prefer to think of it in an positive light: almost anything could be possible. $\endgroup$
    – Dan
    Commented Dec 28, 2018 at 15:57

2 Answers 2

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Welcome to Worldbuilding!

First, the planet itself does not need to be tidally locked. Either scenario is plausible. It depends on the history of the planet's formation. Even Mercury itself isn't tidally locked. So, it's up to you.

If you do decide you want your planet to be tidally locked, then:

  • It can have a moon, but the orbit of said moon would be at risk of destabilizing over a very, very long period of time. Eventually it could fall into the planet, opposite of what is happening with our own moon right now. (Potential plot point?)
  • The climate of a tidally-locked planet's habitable zone may be wildly unstable. However, this mainly depends on a) the composition of the atmosphere and surface rock, and b) the surface conditions at the subsolar point, especially vis-a-vis liquid water. I can elaborate on this with more information on your planet's environment.

As far as size goes (regardless of whether it's tidally locked), the planet can be very small, like Mercury, or several times larger than the Earth. Again, it's up to you. Scientists have found massive rocky planets closer to their parent stars than the Earth is to the Sun. Here's a recently discovered example of one such planet.

As for the flora: According to this source, you might expect the color of flora to naturally appear "red, blue, yellow, purple, or even grayish-black." Interestingly, that article mainly discusses planets orbiting binary stars, postulating their flora might appear black to us. In any case, it depends on the amount of light the plants receive and their chemical make-up. I would wager that dark-ish blue, purple, and gray colors would be more than acceptable, though I would recommend against having one single uniform color throughout the entire world. (Keep in mind the vast variety of plant life colors here on Earth, for comparison.)

Finally, the appearance of the sky depends on a lot of things, including (but not limited to) the composition of the gases in the atmosphere, dust in the air, distance from the star, etc. I'll gladly edit my answer if you provide more details in your question. Or, if you already have in mind a particular way you want the sky to look, I can attempt to give you conditions that might produce it.

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  • $\begingroup$ Thank you for your answer, really, and sorry for not replying sooner, I couldn't get the account back easily, and honestly I didn't think this community was so active, I'm very glad it is. $\endgroup$
    – Hans
    Commented Jan 1, 2019 at 16:37
  • $\begingroup$ About your answer: It doesn't need to be tidally locked, so if it's such a problem, I won't do it. I thought black because I was imagining they receiving less light from the sun, and of course, not all will be black, just most of them and not jet black too, just black-ish. phet.colorado.edu/sims/blackbody-spectrum/… a red sky seems good, not sure about sunset though. And how would be the night and day system? could it be similar to Earth's? How would the moon be? Again, thank you. $\endgroup$
    – Hans
    Commented Jan 1, 2019 at 16:46
  • $\begingroup$ @Guy You're very welcome. Whether it's tidally locked is up to you; either way is possible so go with whatever you prefer. If the planet is not tidally locked, and you want a system similar to Earth's with a similar sized moon, then go right ahead. The main difference will be how quickly the planet orbits and rotates. If you tell me how long you want your days and years to last, we could come up with a reasonable estimation. $\endgroup$
    – Dan
    Commented Jan 1, 2019 at 16:55
  • $\begingroup$ @Guy Second, sorry if I wasn't clear on plant colors. Here on Earth, the chemical makeup of a plant determines what parts of the spectrum get absorbed. I'm not botany expert, but from what I do know, I see no reason at this point why your plants couldn't have evolved to absorb light in a way that makes them appear black. $\endgroup$
    – Dan
    Commented Jan 1, 2019 at 17:13
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    $\begingroup$ They do, it shouldn't be a problem. I said it many times already, but thank you very much, english isn't my first language and this is going to be my first story, so it will most likely be really bad and no one(except my friend) will read it, but as bill wurtz said in his "long long long journey" song "If I came here to lose, then I still might win." Wish you the best. $\endgroup$
    – Hans
    Commented Jan 3, 2019 at 3:33
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"What are the complications the inhabitants of such a planet face?"

Well, since the planet is tidally locked (and as long as it's been so for at least thousands of years), the sunny side would likely experience tropical temperatures year-round, or even hotter. and would be mostly overtaken by an ocean with small archipelagos scattered around.

The vegetation on a brighter side might evolve to be whiter, as it doesn't require that much sun to grow and thus needs to bounce some away. The opposite could be true for the dark side, although plants would likely not even exist at all and might be completely overtaken by a massive ice sheet.

Since there are virtually no seasons or things of the like, animals wouldn't migrate, weather would be extremely predictable, and farms would be widespread and easy to grow. Life on the bright side would evolve quickly, while those on the dark side would likely die out quickly.

"Apparently it doesn't have to be tidally locked, but I didn't understand how that works, apparently it would have to have some kind of moon orbiting around it?"

I can't really see how that'd be true. Since the planet would have to be really close to the red dwarf (since the star is small and thus has a closer habitable zone), the tidal forces acting on the planet would be much stronger than Earth's and would pretty much force it into being tidally locked.

"If you want to show off your knowledge and tell me how the sky would appear...I'll be impressed."

The appearance of the sky essentially depends on how dense the planet's atmosphere is. Earth's is blue because of the high amounts of gases. The gas particles completely absorb most short-wavelength colors, like blue, which scatters them (basically radiating blue out in all directions from the particle). Since blue is one of the most scattered colors, the sky appears blue because blue light is constantly hitting the gas particles.

It could also depend on the range of colors emitted by the star. The Sun would appear white if you were to be suspended in space without the atmosphere to color it, and so it emits virtually all light on the color spectrum. If the star emits only reds and oranges, the atmosphere would be predisposed to being in that range.

I don't know how dense your planet's atmosphere is, but the less dense it is, the darker and fainter it would be. Since it orbits a red dwarf, the sky would likely be orange or even yellow.

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  • $\begingroup$ This description doesn't jive with our best models. In all likelihood, the sunny side would be so hot that it's questionable whether there'd be surface water on that side whatsoever. As for tidal locking, it's not a given that it would be locked (it's possible, of course, but not a certainty). Also, the weather could in fact be extremely unpredictable, depending. Lastly, the plant colors you laid out are probably backwards. (I posted links about those last two points in my answer you might find interesting.) $\endgroup$
    – Dan
    Commented Dec 30, 2018 at 6:30
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    $\begingroup$ All that said, I don't want to sound so negative. Your points about the atmosphere are good. But your description of the surface is unfortunately too picturesque according to the best models we have today. But in spite of that, anything is possible. It's interesting to try and conceive plausible conditions for the environment you've described, perhaps something on the outer fringes of the Goldilocks zone with particularly favorable atmospheric and landscape characteristics of some sort which we haven't generally accounted for.... $\endgroup$
    – Dan
    Commented Dec 30, 2018 at 6:43
  • $\begingroup$ Thanks. I thought some of the points seemed off, but most of them were taken from a science-based website (although I can't remember the URL). The plant colors made sense to me simply because it's a commonly-known fact that white reflects more sunlight while black absorbs more, but I can definitely see your point. $\endgroup$
    – kineticcrusher
    Commented Dec 30, 2018 at 17:39
  • $\begingroup$ Yeah, the plant thing totally seemed counterintuitive at first to me, too. $\endgroup$
    – Dan
    Commented Dec 30, 2018 at 17:54
  • $\begingroup$ Thanks for the answers guys, If tidally locked, I wanted them to be in a cold environment, which give me 2 options, either putting the planet a bit farther away from the star, or moving their living place a bit closer to the dark side, the first seems more complicated(or not?), I thought black because I was considering moving the planet, and in my logic, somehow, the light reaching the plants would be fainter and the habitable zone would be colder, making the plants darker to absorb more light, does it make sense? $\endgroup$
    – Hans
    Commented Jan 1, 2019 at 16:53

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