Deep beneath the ice-crust of Europa, lies its famous subsurface ocean. Having existed for billions of years, this ocean now harbours a huge range of life forms on its sea floor.

However, in trying to design some of these life forms, I have run into a problem: I would like all the major phyla of europan life forms to possess infra-red vision, capable of detecting differences in heat of as little as 0.001 degrees from up to 5 metres away. But I am struggling to design an organ capable of doing this.

What hypothetical organ could reach the limits described above, and how would it be structured?

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    $\begingroup$ There's a significant problem with this idea. Water absorbs infrared rather well: it is pretty well blocked by two meters of water. The very high heat capacity of water also tends to make everything immersed in it end up at the same temperature as the water, so there isn't much to see in the infra-red. $\endgroup$ Feb 19 at 17:27
  • $\begingroup$ We have real life examples of fish that can literally see infrared. In your case however, it hardly sounds useful, since we're talking about animals living in a pitch black and likely freezing cold oceans where such temperature differences would probably be nigh undetectable unless they got really close to the prey. At this point, electroreception and echolocation are probably much more advantageous, since even a fish that causes virtually no temperature change in the water can't escape a sonar, or hide the electric impulses it needs to do anything. $\endgroup$ Feb 22 at 4:14

1 Answer 1


Look at pit vipers:

The ability to sense infrared thermal radiation evolved independently in two different groups of snakes, one consisting of the families Boidae (boas) and Pythonidae (pythons), the other of the family Crotalinae (pit vipers). What is commonly called a pit organ allows these animals to essentially "see" radiant heat at wavelengths between 5 and 30 μm. The more advanced infrared sense of pit vipers allows these animals to strike prey accurately even in the absence of light, and detect warm objects from several meters away.

[...] In pit vipers, the heat pit consists of a deep pocket in the rostrum with a membrane stretched across it. Behind the membrane, an air-filled chamber provides air contact on either side of the membrane. The pit membrane is highly vascular and heavily innervated with numerous heat-sensitive receptors formed from terminal masses of the trigeminal nerve (terminal nerve masses, or TNMs). The receptors are therefore not discrete cells, but a part of the trigeminal nerve itself.

[...]The sensitivity of the nerve fibers is estimated to be >0.001 °C.

  • $\begingroup$ Are they called pit vipers because they live in pits? Or because they have pits on their face? We will never know! $\endgroup$
    – Daron
    Feb 19 at 17:33

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