2
$\begingroup$

Question in the title. A Rogue planet is a sunless world that exists in interstellar space. It might be possible for life to develop on one, but what happens when that happens?

I've seen people say that plants could not develop on these worlds. But there's the theory of Thermosynthesis, which is almost what I'm looking for. But would it be possible to absorb infrared photons? What is the most efficient color to absorb infrared light? I've heard different things about nonvisible light's albedo, and can find nothing to confirm one way or another.

I saw this, and I can see nowhere on it that mentions the color of plants.

$\endgroup$
  • 1
    $\begingroup$ Plant and fauna on Earth can have leaves of a huge variety of colors. There is no reason to consider this less likely elsewhere. However I'd direct you to the answer by Ville Niemi for why there's a basic problem with thermosynthesis. $\endgroup$ – StephenG Jan 18 '18 at 8:32
  • $\begingroup$ There have been several questions about plant color on hypothetical planets and the answer is always the same, any color you want. The color of plants is an accident, a quirk of history, not an adaptation, any color save white will work for photosynthesis. worldbuilding.stackexchange.com/questions/33915/… and worldbuilding.stackexchange.com/questions/63259/… $\endgroup$ – John Jan 18 '18 at 15:50
5
$\begingroup$

In a world like that the primary sources of energy for organisms would be chemosynthesis or, hypothetically, thermosynthesis. Neither relies on electromagnetic radiation and as such have no effect on the color of the organisms.

As such organisms would have no pigmentation as such and would probably be colourless or transparent "things" living in lightless subsurface oceans. You can look for speculation on possible life forms on Europa (“ALL THESE WORLDS ARE YOURS, EXCEPT EUROPA. ATTEMPT NO LANDING THERE.") for inspiration.

Absorbing infrared photons would not really work. Photosynthesis relies on receiving photons from higher energy level than your ambient energy level. This is the energy flux that does chemical work. Receiving photons from your own or lower energy level is not really useful as it cannot generate a positive energy flux that does work. The exception would be scavenging waste energy from your own energetic processes. Typically we would be talking about power plants, engines, chemical factories, or high performance micro-processors, not life forms.

$\endgroup$
  • $\begingroup$ Love the 2001 reference. $\endgroup$ – Renan Jan 18 '18 at 13:47
4
$\begingroup$

Plants on the surface of the Earth appear green to our eyes because they're reflecting the green spectrum and absorbing (basically) everything else ... including infrared.

If we look to plants surrounding geothermal vents we find a wide variety of colors, I expect that is because they evolved to rely on something other than sunlight to provide the energy they need.

A rogue planet has a similar problem.

  • Some plants may evolve to take advantage of what radiative energy exists in the void. As these plants have no dependency on visible-spectrum light, I would expect them to develop a wide array of colors depending on their chemical composition (assuming they could withstand the visible light spectrum). I expect this would mean the same plant located in an iron-rich soil would be more red than a plant in a magnesium-rich soil (white) or a plant in a cobalt-rich soil (blue).

  • It should be noted that on a rogue planet, plants are more likely to evolve to take advantage of a wider array of energies (including geothermal) than was necessary on Earth. As with all things, evolution tends to take the path of least resistance. An abundance of sunlight would preclude the evolution of chemically-dependent coloration.

Except for flowers, of course... and the red-barked dogwood. Ware all ye who adventure beyond the void, the red-barked dogwood....

$\endgroup$
  • 1
    $\begingroup$ Green is only the dominant color in earth plants by accident, any color could have (and in many cases did) evolved. $\endgroup$ – John Jan 18 '18 at 15:40
3
$\begingroup$

There is no evolutionary advantage to evolving pigmentation (for the visible spectrum) if there is no source of visible light. "Thermoflora" would be whatever colour is innate to their molecular substrate. Colour also does not play a factor in absorbing or permitting infrared, so your plant's appearance will be dictated by the wavelength-blocking materials their surfaces are made of.

If you want to get really alien, leaves of vanadium and sapphire would be one of the most efficient absorbers nature could hope to produce – sapphire blue and grey suspended in layers within the leaf structure.

$\endgroup$
0
$\begingroup$

I have heard a theory that on such a rogue planet the radiation from transuranics or anything radioactive would be used as an alternative to sunlight. This may seem weird, but there are Earth fungi that can do the same thing (Google it. It's weird how easy it is to find stuff on them). I'm guessing such lifeforms wouldn't have any particular color at all but just focus on moving through the ground, looking for more radioactive ore to feed on, like slime mold seeking food.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.