I'm building an alien world for an artistic project. The world circles an m-dwarf star, and so the flora have evolved to photosynthesize longer wavelengths of light than on Earth, primarily in the near infra-red. I've come up with an interesting symbiotic relationship, however I don't know if its scientifically plausible. Here's how I think it might work...

Plants have evolved to make use of the near-infrared, with peak photosynthesis at around 1045nm. In my postulated symbiosis, the plant has evolved to feed on the infra-red radiation emitted by small animals in addition to the sunlight. During the day the plant turns its "leaves" outward towards the sun, but at night the leaves curl inward, through holes into a chamber within its "trunk." The chamber has evolved to provide a comfortable and attractive nesting habitat for small animals that in turn not only produce infrared for the plant to photosynthesize, but also disseminate the plants "seeds."

The big questions here...

Could an organism (the plant) evolve to make use of the the infrared photons a warm-bodied creature produces? And would it be advantageous? I'm skeptical, since the difference between the near-infrared used from the sunlight on this world (1045nm) and body heat (maybe 10,000nm?) is huge. One order of magnitude. If it could work, how? Would it be through "normal" photosynthesis in which the plant utilizes a larger number of infrared photons to drive the photosynthetic reaction (i.e. many more photons needed for the same energy). Or perhaps the body heat would help the plant drive a completely new chemical reaction that isn't photosynthesis as we know it?

If the plant can't evolve far enough in that direction, could the animal evolve to produce much higher wavelength radiation, perhaps as a normal by-product of its metabolism? So perhaps instead of emitting just "body heat" at lets say 10,000nm, maybe it evolves some beneficial or neutral chemical reactions to produce radiation at let's say...2,000nm, which might be a more plausible wavelength for the plant to adapt to utilize. I have zero idea on how that might work. I don't really even fully understand why humans chiefly emit at around 10,000nm, much less what the plausible range of emissions could be as a by-product of metabolic processes.

I'm okay with any ideas from the spitballed to the highly researched. :)

Thanks guys!

Edit: I've been getting some comments on there not being enough energy from the star to fuel complex plant life. This is not the case. The planet I'm working on is close enough to the star to receive more energy than the Earth does, however that energy distribution is strongly titled into the infrared. The planet would seem slightly dim to Earth eyes, but it's far from dark or lacking energy. The salient issue are the really long days/nights (let's say 13 Earth days of night per rotation). I figure there is plenty of opportunity here for plants to evolve other mechanisms for extracting energy from their environment during the many many dark hours.

Second Edit: Instead of thinking about this problem in terms of light/photons, what if we just consider it in terms of making use of available thermal energy? The animal is warm, the plant cold, the animal is inside the plant, therefore the plant WILL heat up, creating a thermal gradient from the interior outward. It seems like there could plausibly be some sort of beneficial biological work that could be done with this extra heat energy. Or am I thinking about this all wrong?

  • $\begingroup$ I think this question can very well be answered, but I wonder what your level of education is. Since you are writing biochemical fiction but asking about things that any university level student should know, I'm a bit confused. Please don't see this as an attack, but how useful is an answer if you do not understand it? Here are things that throw me of: You know a lot about the spectrum, however you have not googled how much heat animals radiate. You also are aware of photochemistry but apparently not about how different parts of the EM spectrum interact with molecules $\endgroup$
    – Raditz_35
    Commented Feb 14, 2018 at 16:48
  • $\begingroup$ And PS, maybe the most important thing: "Would it be through "normal" photosynthesis in which the plant utilizes a larger number of infrared photons to drive the photosynthetic reaction (i.e. many more photons needed for the same energy)." Are you aware of quantum physics? $\endgroup$
    – Raditz_35
    Commented Feb 14, 2018 at 16:50
  • $\begingroup$ @Raditz_35 A human's radiation peaks at about 10,000nm according to Wikipedia. I assume most warm-bodied animals on Earth would peak similarly. My level of science education is "well read." I have no science degree, but I would wager I know more than 95% of the general populace. I don't know very much about this particular topic. It's rather....esoteric. $\endgroup$
    – n_bandit
    Commented Feb 14, 2018 at 17:06
  • $\begingroup$ @Raditz_35 I'm not sure I understand your quantum physics question. $\endgroup$
    – n_bandit
    Commented Feb 14, 2018 at 17:07
  • $\begingroup$ A general rule of thumb is that for every 10 units of energy an animal consumes, it outputs 1 unit of energy. Are the animals surviving by using the plants as a food source? If they are the plants are getting a pretty rough deal, (they're getting 100 calories worth of leaves being eaten for every 10 calories of heat they get back). $\endgroup$
    – Hans Z
    Commented Feb 14, 2018 at 17:10

2 Answers 2


No on both.

Having a plant that can survive on "waste radiation" of an animal would imply the animal is ridiculously inefficient. After all there is this huge fusion furnace in the sky and the animal still counts as a viable radiation source. Such animal would be unlikely to survive and extremely unlikely to evolve naturally. You could of course hand wave some sort of micro fusion or magical energy that animals have but plants do not but that seems non-optimal.

Also note that photon energy is inversely proportional to wavelength. Without going to too much detail this means that converting long wavelength radiation to chemical energy is very hard. Optimally you would want to use radiation where photon energy is very close to the energy of the chemical reaction you want to use and to use fairly energy dense compounds. It is doable with lower photon energies but the needed structures would be larger and more complex and their evolution would be hard to explain.

  • $\begingroup$ You make very good points. However, is body heat really just "waste" radiation? By that logic, the more heat an animal outputs the less efficient it's metabolic processes. So a purely efficient animal would then (logically) emit zero body heat. This doesn't sound right to me. Humans emit more body heat than lizards, but I doubt humans are "less efficient" than all lizards. Another question is...could the animal output the same amount of energy, but "step it up" so that the the energy emitted is the same, but packed into fewer higher energy photons. $\endgroup$
    – n_bandit
    Commented Feb 17, 2018 at 1:47
  • $\begingroup$ Perhaps thinking about it in terms of "light" and photons isn't the only lens...what about just movement of energy? Basically wherever there is a discrepancy in temperature there is the potential for converting that discrepancy into some kind of work. In this case some type of molecular work. The plant is colder than the animal it contains, so as the animal sheds heat, it could capture the heat, perhaps even very efficiently. That seems reasonable. Now, if the heat is captured it should be able to power SOME type of chemical process. If not photosynthesis some other beneficial process? $\endgroup$
    – n_bandit
    Commented Feb 17, 2018 at 1:54
  • $\begingroup$ @n_bandit Humans are less efficient because we maintain a stable body temperature which generally has a temperature differential with the ambient. This consumes energy. Unfortunately the efficiencies of spending work to create the differential and getting work from the differential are both related to the magnitude of the differential but in the opposing directions so efficiency with one requires inefficiency with the other. $\endgroup$ Commented Feb 17, 2018 at 11:16

Not via infrared

Chlorophyll absorbs in the 400-700nm range. Anything outside it is not absorbed and is therefore not useful (conventionally speaking). So already at 1000nm you are looking at useless light that most plants cannot absorb. Also bear in mind that absorption is not 100% effective so even if you somehow get energy landing on the leaf that it can use, you are still looking at only about 0.1-2% sunlight-to-biomass efficiency. https://en.wikipedia.org/wiki/Photosynthetic_efficiency

There is some special chlorophyll that can maybe absorb a tiny bity of very high energy infrared but again its no where near your numbers. https://www.wired.com/2010/08/infrared-chlorophyl/


You also have the problem of as your energy source becomes less and less, the complexity of life it can support also becomes less and less. You're world is more likely to look like a giant sea of algae than a system with trees and wildlife.

Your plant should just eat the little woodland creatures instead if they exist. Or maybe your plant can eat the poop of your little friendly woodland creatures, or eat the leftovers of their meals if they are meat eaters? This might be one symbiosis idea. The creatures bring food into the plant and live there, the plant eats the leftovers? Or maybe your alien squirrels have a lot of parasites and your plant has a nectar that draws those out off the alien squirrels and then proceeds to eat the parasites? Home and pest control, yay!

There are obvious other problems with predicting what life will look like on a low energy planet (probably nothing like earth), but if you need symbiosis for your writing and somehow the world got to the point where there are trees and wildlife, and you WANT them to have symbiosis with wildlife, I think the above ideas probably work.

  • 1
    $\begingroup$ "860 W a day" is meaningless word salad. And in general, a human must dissipate just about the same amount of energy that they consume; since a human consumes some 2000 kcal (8.37 MJ) per day, it follows that they must dissipate about 8.37 MJ / 86400 s = 100 W. Some of those 100 W are dissipated by convection, some by evaporative cooling, and the balance by infrared radiation. No need for atrociously mangled fancy equations. $\endgroup$
    – AlexP
    Commented Feb 14, 2018 at 20:32
  • $\begingroup$ Why do you assume this species works with chlorophyll? Certainly chlorophyll can be used for photosynthesis, but what about some other chemical with similar function? Considering chlorophyll is ineffective it shouldn't become that much of a preferable trait in the ecosystem to begin with. $\endgroup$
    – Wel Wyrmin
    Commented Feb 14, 2018 at 20:39
  • $\begingroup$ Regarding the wavelength/chlorophyl question, I believe you're correct on the the wavelengths chlorophyll absorbs. However chlorophyl isn't the only compound Earth plants use to absorb photons. According to this paper from the NASA Goddard Institute for Space Studies there are some earth plants which absorb up to about 1000nm (cant recall exact number). It also mentions there is no theoretical reason shorter wavelength (1200, 1400, etc.) photons couldn't be used. The energy imparted would simply be less per photon. Link: ebscohost.com/uploads/imported/thisTopic-dbTopic-1033.pdf $\endgroup$
    – n_bandit
    Commented Feb 14, 2018 at 20:48
  • $\begingroup$ I do like the poop/leftovers/parasite ideas. Not direct answers to my question, but solid ideas in their own right. $\endgroup$
    – n_bandit
    Commented Feb 14, 2018 at 21:07
  • $\begingroup$ Well in the case of photons not in the stated chlorophyll range, one reason they are not absorbed is that they are instead reflected. But from another perspective, there is also a minimum amount of energy needed to trigger a chemical reaction. This is another problem. A trillion photons below the required thresh hold doesn't help any, because none of them triggered the reaction. $\endgroup$ Commented Feb 14, 2018 at 21:20

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