So i want to create a planet that supports human life. Primarily, i would need to consider a star type, an atmosphere, foliage pigment, and potentially different types of plants. Think of it as a sort of alternative environment to earth in a way if it helps understand the question. Mostly everything else about earth would likely still apply, such as gravity, mass, temperature, etc.

Currently, i'm heavily interested in a foliage pigment that reflects blue light the most, giving plants a blue color. I also would be curious as to whether prominent fungi would be possible (giant tree-sized fungi, perhaps in certain areas in the planet coexisting with traditional foliage). I initially figured the star type would need to be an F-type star because that emits the most amount of blue light, hence plants would likely reflect that to avoid sunburn. Problem with that though is i don't have a good grasp as how that would affect human habitability or the sky color even (it would probably have to still be primarily oxygen and nitrogen to support human life).

I guess to put it simply - What would an earth-like planet's star-type need to be, sky color, how would fungi be affected (and would it be possible for them to grow to tree-like sizes), if the foliage pigments were to primarily reflect blue light and the planet were required to support human life?

  • $\begingroup$ the color of a plant's photopigment depends on what color of light the star peaks at. on earth, plants are green because the sun peaks in green and they want to avoid having too much radiation, so they reflect green. plants could have been purple instead though, evolving to absorb the light thats produced the most and avoid taking in too much radiation by reflecting all other colors. $\endgroup$ – zackit Mar 1 at 18:13
  • $\begingroup$ if you want blue plants, you'll want a very dim, red dwarf or orange dwarf star to avoid the problem of plants favoring bluer light due to it having more useable energy. if you have a blue star, you can have cyan plants. the red and orange will make plants either be blue or yellow, most likely yellow. $\endgroup$ – zackit Mar 1 at 18:18
  • $\begingroup$ fungi sizes are decided more by the amount of CO2 and oxygen in the atmosphere, if you want fungus the size of trees, you'll want as much of both oxygen and CO2 as possible to increase their carrying capacity, as well as a high energy star. this doesnt work well with blue plants though, due to blue plants being more common with lower energy stars, so in order to compensate you would need much higher O2 and CO2, high enough that humans cant survive. alternatively, make the planet have much lower gravity so the oxygen and co2 requirements are lower. $\endgroup$ – zackit Mar 1 at 18:39
  • $\begingroup$ I have read that blue plants may also grow in bright blue stars if they evolved to reject blue light and instead absorb other pigments, because absorbing the blue light would cause it to sunburn easily, though i don't know how accurate this information is. Maybe if this information was accurate it could open up some potential for fungi to coexist with blue plants as per your third comment? $\endgroup$ – plasmawario Mar 1 at 19:28
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    $\begingroup$ @zackit: "Plants are green because the sun peaks in green and they want to avoid having too much radiation": No, that's not true. It's a simple just-so story. (Most) land plants are green because they are descended from gree algae. Were land plants descended from red algae, or brown algae, or blue algae, they would be red, or brown or turquoise. It's an evolutionary accident. And anyway, not all land plants are green. Some are purple. $\endgroup$ – AlexP Mar 1 at 20:22

What would an earth-like planet's star-type need to be,

This is less relevant than you might expect. After all, green isn't really the optimum colour for photosynthesis on Earth... its just good enough. It isn't so great that there aren't several other colours and flavours of photosynthetic organism that work well enough that they haven't simply been outcompeted. Accessory pigments have evolved in some organisms to help deal with chlorophyll's inadequacies, including absorbing green light that would otherwise go to waste.

I will say that hotter, brighter stars than our own are likely to be quite hostile to life... much more UV, faster spinning, shorter lived, that sort of thing. Cooler orange stars would have less blue and green light, but vegetation there could still be green and photosynthesise just fine. Hell, they might even be able to get away with our own flavours of chlorophyll, with suitable accessory pigments, as they can absorb red light well enough.

So, take home message: if you want blue plants, you've got em. You don't need a radically different star and planet to put them on.

sky color,

This is largely influenced by the thickness of the atmosphere, and the gases it is composed of. There are other questions on this site about sky colour, but if you have a largely nitrogen/oxygen atmosphere, it'll probably look quite like our own sky.

how would fungi be affected

Probably not at all.

(and would it be possible for them to grow to tree-like sizes)

This is a different question altogether really, but I'll give you a quick answer: no.

Fungi don't need to grow to gigantic sizes. They live where the food is, and as they don't need sunlight there's not much need to poke their heads up unless they're chucking spores around, which doesn't need tree-sized structures to do.

Prototaxites were previously thought to be giant fungi, but more recently have been discovered to be more like lichen which is photosynthetic and therefore benefits from aerial canopies. They failed to compete with trees though, so it seems a little dubious for giant lichen and trees to coexist.

  • $\begingroup$ For your section regarding the star color remaining largely the same due to bright blue stars emitting too much harmful UV radiation, would a slightly different ozone layer help with absorbing the excess UV radiation solve this (i'd imagine a thicker ozone layer would result in the planet needing to be farther away which isn't a problem)? $\endgroup$ – plasmawario Mar 2 at 22:56
  • $\begingroup$ @plasmawario ozone can't help you here as it isn't the surface that you need to protect. The problem you face when your atmosphere is bombarded by ionising radiation is that the top layers escape much more quickly so the odds of you hanging on to your atmosphere for long enough to evolve a biosphere are somewhat reduced. I'm not sure at what sort of stellar temperature this becomes a serious issue, so there's some wiggle room here. $\endgroup$ – Starfish Prime Mar 3 at 8:23

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