# Can just heat be used to power ATP production?

I want to have some lifeforms that live around and in hot environments and absorb the heat around them to produce ATP without using any other energy sources. Is this possible? How can this be done? Can a temperature of 40 C power enough ATP production for life?

• @L.Dutch has it right; heat is energy lost to entropy. The only way heat can do work is if there is a cold sink for the heat energy. With no differential, absorbing heat to do work reverses entropy, meaning that it requires energy to do so. Commented Jun 10, 2023 at 8:05
• You will likely find this link interesting
– M S
Commented Jun 10, 2023 at 8:55
• Aren't the hydrothermal vent ecosystems a well-known real biology example? Commented Jun 10, 2023 at 9:40
• @AlexP hydrothermal vent worms use chemicals present in the erupting vent water, not the heat itself.
– John
Commented Jun 10, 2023 at 12:49
• ATP is a (very complex) chemical. Where do your lifeforms get the carbon, hydrogen, oxygen and phosphorous? Commented Jun 11, 2023 at 9:53

No, heat alone can't power any engine.

If you had a high temperature reserve and a low temperature reserve, you could extract part of the energy difference between the two as useful work, with a maximum theoretical yield given by Carnot $$\eta = 1 - T_{low}/T_{high}=(T_{high}-T_{low})/T_{high}$$.

But having only high temperatures won't be enough.

• Just as an explainer for the OP, not just an engine, but anything at all.
– user86462
Commented Jun 10, 2023 at 8:27
• @AncientGiantPottedPlant the thermodynamics are the same, metabolism is basically a biological engine.
– John
Commented Jun 10, 2023 at 12:52
• @John That's what I said
– user86462
Commented Jun 10, 2023 at 19:13

If you consider temperature alone, the answer is no, as explained by L.Dutch. You cannot convert thermal agitation alone in energy, you'll need at least a thermal gradient for that.

Meanwhile, if you consider supporting exotic life with a non-visible light radiative source, you should consider the infrareds.

They are emitted by many hot objects (including the human body) and have many interesting properties. Among other, they are able to go through organic tissues for several centimeters, hence depositing their energy more homogeneously. This make them an ideal source for gentle warming of organism, see these infrared-powered chicks below :3

When considering Earth lifeforms, infrared can stimulate the mitochondrias. Mitochondrias are the 'power plants' of our cells, and use a complex machinery to generate ATP, the 'carburant' of the cell. Infrared light is known not only to be efficient in warming chicks and pups, but also to enhance cell repair (i.e. cicatrisation) and metabolism overall, and even lifespan in some extents.

Also, it is known that on Earth, plants can use infrareds as an energy source in shady environments. The main drawback of infrareds vs visible light is that they are less energetic, thus your lifeforms would have a slower metabolism than on Earth.

Significant natural infrared sources could be any high-temperature object, including stars (you may prefer a red dwarf) and lava.

• Heya, could bacteriochlorophyll absorb infrared radiation from surrounding heat and use it to produce ATP? Would it be enough energy to power maybe a bacterium? Commented Jun 10, 2023 at 14:41
• @GrimmReaper18B I'd say possibly, but the bacterium still pretty much needs to be at a lower temperature than the IR source. There's no way to get around the Carnot efficiency cited in L.Dutch's answer. The bacterium could be kept cool by the air (if there's a cool breeze), or by radiating IR into space (if it can see the sky), or by emitting IR at wavelengths where the source is transparent (if the source itself also only emits IR at certain wavelengths, and is transparent at others). Commented Jun 11, 2023 at 0:58