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Imagine a planet where there are extremely cold temperatures and water can be found only in frozen state.

To cope with harsh conditions the creature evolved so it can melt ice with its body surface and through that process gets liquid water which it needs to survive. Through this process the creature can melt liters of water in mere minutes. How can I explain extreme heat radiation from body surface so it is at least somewhat realistic and backed up with science and laws of nature.

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    $\begingroup$ Have you ever touched ice with your own hands? $\endgroup$ – dot_Sp0T Oct 23 '17 at 22:28
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    $\begingroup$ Doesn’t sound like a very good evolutionary strategy to me. It would be far better to eat the ice and melt it internally. Using your hands is going to waste heat hand over fist (literally). The big issue here is energy usage. If there is sufficient energy available then it’s probably doable. $\endgroup$ – Slarty Oct 23 '17 at 22:37
  • $\begingroup$ A creature with enough un-insulated surface to melt and collect water in a cold climate will need a lot of calories. It will be quite the dangerous, always-hungry predator. $\endgroup$ – user535733 Oct 23 '17 at 23:45
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    $\begingroup$ I can melt an ice cube in a few minutes with my bare hands or by putting it in my mouth. Seems that humans have already adapted to this. $\endgroup$ – Christia Oct 24 '17 at 2:16
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    $\begingroup$ As others have already pointed out: there is so much wrong with this if you want any kind of realism. Rule #1 to survive in extreme cold: do not let the heat out. Having some kind of heating element in its hands is a tremendous waste of energy. Ok, not so say that evolution does not make its mistakes because it only goes with the fittest, not the most optimal possible solution for the situation at hand. But this concept puts such a huge strain on the willing suspension of disbelief that I would say that @Slarty has a much better solution: eat the snow/ice and melt it in the body. $\endgroup$ – MichaelK Oct 24 '17 at 8:33
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To melt 1 kg of ice at 0℃ and get water at 0°C you need about 334 kJ. To do it in a minute requires 5.6 kW of power. Skin-water heat transfer coefficient is, if I understand correctly, up to 90 W / m² ∙ K. Let's assume big hands, one square meter of skin. And coefficient a bit bigger, of 100 W / m² ∙ K. This seems surprisingly doable — you would need only about 56°C at the skin surface to melt your block. It is only 16°C higher than mammals can do. Of course, if someone could check my math I will be grateful.

There is, of course, problem with supplying energy like that. 334 kJ = 80 kcal. But biological organisms tends to have efficiency much lower than 100%. Eating about 200 kcal to just melt 1 liter of water? Humans need, on average, 2000 to 3000 kcal and 2 liters of water. So for something like us, melting water that way would use up 1⁄5 of our usual calories intake. For creature lurking on an ice world this might be an issue.

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  • $\begingroup$ Actually, it looks pretty good the way you did it without the MathJax. I improved the presentation a little using thin and hair spaces. The only real ugly part is the use of °C in the units, and TeX probably doesn’t help the weird spacing, and using stand-alone ° symbol would let you match the font of the C. I’ll wait a few minutes and then change the units to use K instead, so it won’t merge the changes into one. You can review and roll back that if you prefer. $\endgroup$ – JDługosz Oct 24 '17 at 8:47
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    $\begingroup$ Interesting… Firefox (I assume the client end, not S.E.) formats the numbers on either side of the fraction slash character U+2044. 1⁄5 for example. There is a char for 1/5 directly too: ⅕ but I know it has compatibility problems showing on Android. $\endgroup$ – JDługosz Oct 24 '17 at 9:09
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Have your creature develop metallic skin

By having reflective skin, you will limit the heat radiated to the surrounding environment. You do not need extremely hot body to achieve what you want, but you will be able to explain why your creature doesn't melt all nearby ice while they move when they are hot.

They can't walk on frozen lake, though.

In short, metallic skin prevents heat radiation, but promotes heat conduction.

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It could be possible by giving the animals a high body temperature, but I don't think it's very realistic because they need so much energy to reach that temperature. This can be fixed by giving them a very good digestive system that gets almost all energy out of the food. If they have fire they can maybe warm up at the fire so they can smelt the ice later, but then they'd just use the fire. So I think it is possible, but very unlikely

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