So I was designing some aliens who exhale colder air that they take in and one person gave me a really great suggestion, using phase change materials in the creature's make up to absorb the heat from the air. When looking into phase change materials I saw that GeSb$_2$Te$_4$ is one that can also hold data (not sure if that would come in handy or not) but my though process was, hey Germanium is similar to carbon and if silicon being similar to carbon and can be incorporated into some micro organisms maybe Germanium can, while bonded with the other two elements in order to make the phase change creature possible.

So my question is can GeSb$_2$Te$_4$ be used as the basis for a biochemistry to reasonably accomplish this goal, and if not would their be a better alternative (preferably using hydrocarbons)?

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    $\begingroup$ You are mixing up concepts: not all carbon containing molecules are organic, take limestone CaCO3. Same for your material.... $\endgroup$
    – L.Dutch
    Commented Feb 16, 2018 at 13:35
  • $\begingroup$ @Renan Not a dupe, this is a followup question targeting a specific compound. $\endgroup$
    – kingledion
    Commented Feb 16, 2018 at 18:11
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    $\begingroup$ @kingledion I see. I have retracted my close vote, and will vote to reopen if this one gets closed. $\endgroup$ Commented Feb 16, 2018 at 18:14

3 Answers 3


Use water ice

This creature gains its energy through the Seebeck effect: a difference in temperature causes different current carriers to move apart from each other. The carriers would then be neutralized on both ends; for example, NADPH and ATP are generated by the combined voltage of a thermoelectric pile. The material is then used for things like carbon fixation and production of sugars, or for movement.

The creature would be living alongside somewhere with a very high temperature gradient, or being able to carry a lot of ice at once.

One of such places are ends and side of glaciers. The creature would gorge on glacial ice when at night, move away from the glacier, then uses this stored cold energy to generate usable NADPH and ATP through the Seebeck effect from breathing in warm air. the ice melts, cooling the air that passes through the creature, then the difference of temperature is used to create energy.

The perception that this creature breathes out colder than it breathes in would be an illusion because in the warmer regions, when these creatures came out at day to generate energy, they are most likely to be seen, hunted, or felt.


I don't think that what you are proposing is thermodynamically possible.

If they are cooler than the air, yes, they can even absorb energy from the difference, and both end close to an intermediate temperature.

But, if they are at the same temperature (or even worst, a higher one), they should spend energy in order to make the air cooler. They are fighting against the equilibrium tendency. So, if they are expelling the air cooler than before, they should spend another source of energy (like, chemical), and then get even hotter.

That's why your air conditioning system spends electricity, instead of gaining it.

Edit: There is no useful energy in high temperature, instead it is in temperature difference (see thermoelectric effect, as example). And you can use it when through heat exchange leveling temperatures. So, in order to absorb energy, the two bodies should tend to a intermediate temperature:

Thermal equilibrium Temperature over time

So, there are two options to absorb energy:

  1. The living form is hotter than the air, and both end up closer to an intermediate temperature. Let's say the living form is 38 ºC (and producing heat) and the air is -10 ºC. At some time they may be at 35 ºC and the air at 0ºC, and if they continue to exchange heat to 32 ºC and 10 ºC, and so until both have the same temperature (the numbers are not necessarily realistic). This is not your scenario, because the air get hotter, not colder.
  2. The living form is colder than the air. Is the same thing, but the bodies are reverted. This looks more like your scenario, because the air get colder. But, the living form should be colder than the air previously, and end up hotter than before (but usually not hotter than the air).

The problems with case 2 are:

  1. They should be colder than air before they born, which implies some energy (same or much energy than absorbed). Where did that energy come from?
  2. Eventually they reach air temperature, and can not exchange temperature anymore.

Expand 2, OPTIONS.

  • If you prioritize phase change, you can do it by:
    • Direct conversion of chemical energy (food) into heat.
  • If you prioritize cool air, you can do it by:
    • Enzyme preservation requirement. I imagine a creature that evolves originally at a cold place, but then began to live in each day warmer places (pression to move, maybe because the niche was full, maybe because of climate change). But some very important enzymes can't evolve easily to adapt to new temperatures, so it evolve to preserve a colder temperature at some place of their body at cost of a lot of energy and heating other parts of their body.
    • Two climates adaptation: Similar to previous, but the creature still lives in cold places and from time to time has to move to warmer places. That explains why evolution prioritizes low temperature enzymes, but requires some mechanism that allows to live in "extreme" (for their nature) temperatures as an exception. A cold places can even be the space, although it is more complex*.
    • A strange chemical need of low temperatures, like this one. If they evolve at a low temp. place, it would be hard to change this if they have a critical system/need using this kind of reaction.
    • Other reasons of cold requirement: maybe it has a attack mechanism of freezing their preys and/or defense mech. for freezing their predators.
  • If you want to prioritize both, you have to give up to be science based.
  • $\begingroup$ Well the goal is a cold blooded creature that absorbs the heat and converts it kinetic energy for life sustaining processes and as a result the air it exhales it colder $\endgroup$
    – Amoeba
    Commented Feb 16, 2018 at 1:51
  • $\begingroup$ @user45751 I expand my answer to clarify. $\endgroup$
    – ESL
    Commented Feb 16, 2018 at 12:56
  • $\begingroup$ @ESL couldn't the creature spend additional energy for their refrigerating activity, e.g. energy derived from food? $\endgroup$
    – NofP
    Commented Feb 16, 2018 at 15:11
  • $\begingroup$ Yes. As I explain, you should spend energy to increase temperature difference. But it does not comply with the OP request. I'll expand with options. $\endgroup$
    – ESL
    Commented Feb 16, 2018 at 16:33

You want a better alternative? Here's one that's actually (technically) a Carbohydrate; Ethylene Glycol. Among other things, it's primary use is as radiator coolant in modern society, which when you get right down to it sounds like the kind of thing you would expect a phase change material to be doing.

On top of that, it's also a primary ingredient for some 'smart' PSMs, like your Germanium based one.

There's only one catch; it's toxic to humans. Very toxic actually. What that means is that there would have to be a biochemistry substantially different to human physiology in place for this stuff to function inside a living body, but it's more likely to happen than your Germanium one for several reasons;

1) Availability of the elements
One of the reasons that earth life is carbon based is because there is a lot of carbon, hydrogen, oxygen, nitrogen, iron, etc. in the universe. Because they're common elements, if life can form in the universe, it's far more likely to be carbon based than (say) silicon or germanium based. That means that ethylene glycol (as a CHO compound) is more likely to exist or form naturally on another planet than a compound that includes Germanium, especially in quantities that can sustain a large and thriving biomass.

2) Compounds V. Elements
Put simply, you can do a hell of a lot more in terms of materials diversity if you focus on compounds rather than introducing new elements. If you take a look at most drugs and other substances that have a material impact on our health and / or behaviour, quite a lot of them are CHNO compounds, or some subset thereof. This is because our physiology already uses these elements in various compound formations so the drugs or other substances are designed to interact with our internal chemistry already. Introducing new elements into a carbon based life form only works if those elements can interact with CHNO compounds to create something even newer.

So; what you're suggesting may work, and in fact could be an energy extraction system on a planet where no photosynthesis exists. In such a case, your creature needs energy and may actually be able to directly draw it from a hot planet's atmosphere. In such a case, the physiology may not even be chemical energy based in the conventional form, but may have an internal exothermic reaction that extracts the heat from the ethylene glycol, meaning that it only needs 'food' for nutrition, not for energy.

As such, I can see such a creature existing on the surface of Venus for instance, where the heat and pressure could kill a conventional plant but such a creature as this could exist higher in the stratosphere, converting the heat energy around it to internal body energy and then consuming any nutrition it needs from that same cloud formation.

  • $\begingroup$ Do u think this model could work for a conscious creature and instead uses this ability to function in cold climates while being cold blooded $\endgroup$
    – Amoeba
    Commented Feb 16, 2018 at 0:37
  • $\begingroup$ I was thinking for his sort of creature a planet with weird temperature y can be on either temperature extreme so this adaptation in the creature allows it survive while being cold blooded $\endgroup$
    – Amoeba
    Commented Feb 16, 2018 at 0:38
  • $\begingroup$ Do u think that would work? $\endgroup$
    – Amoeba
    Commented Feb 16, 2018 at 0:41
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    $\begingroup$ I can't see this ability working on cold climates because heat exchange there would be very inefficient; there's not much heat to draw from the atmosphere in the first place. Cold and warm blooded works for us because we use exothermic reactions to draw energy from food, but in this instance I see the model working more as a way to draw latent energy from the environment where heat is more plentiful than chemical energy stores. The creature would probably have a dermal layer saturated with ethylene glycol that then 'feeds' its internal cells. $\endgroup$
    – Tim B II
    Commented Feb 16, 2018 at 1:13
  • $\begingroup$ But could this work for a creature who's reduces the temperature of the air it breaths out $\endgroup$
    – Amoeba
    Commented Feb 16, 2018 at 1:49

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