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It is known that in thermosphere, air temperature is rising sharply with increase of altitude.

In upper atmosphere, temperatures can even reach 2000°C or higher: see 2.

However, air there is extremely thin, so heat transfer is very slow.

If I put an egg to the thermosphere and hold it there for a long time at zero airspeed, will it cook?

Earth Atmosphere Temperature Profile UPDATE: My own line of thought is that the egg may radiate the heat energy faster that acquiring it. But then why doesn't air around it does not radiate it just as well? Answer: Because of the Sun constantly heating it up. But then the egg should be constantly heated up by the Sun as well as the air around it.

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  • $\begingroup$ My own line of thought is that the egg may radiate the heat energy faster that acquiring it. But then why doesn't air around it not radiate it as well? Because of the Sun constantly heating it up. But then the egg should be constantly heated up by the Sun as well as air around it. But if everything is so hot up there, then space satellites must have mostly cooling systems to cool themselves, rather than heating systems, while it doesn't seem to be the common case (except for observatories), are they? $\endgroup$ – Dzmitry Lazerka Jan 26 '16 at 1:28
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    $\begingroup$ Given the air pressure of 0.032Pa at 100km it will dry out before it cooks, I am afraid. You are basically in vacuum up there. How does freeze dried egg taste? Don't know, but could be OK when reconstituted with mayo and mustard... space deviled egg? $\endgroup$ – CuriousOne Jan 26 '16 at 1:45
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    $\begingroup$ @DzmitryLazerka space satellites do have shields to protect themselves from unwanted heating/cooling effects. $\endgroup$ – Bruce Lee Jan 26 '16 at 4:35
  • $\begingroup$ @CuriousOne Yup you are right that the egg would get boiled up at a low temperature. But I am gonna flag your comment as discussions about "space deviled egg" is outside the scope of mainstream physics... :P $\endgroup$ – Bruce Lee Jan 26 '16 at 4:39
  • $\begingroup$ @BruceLee: Yes, you are right, that comment was completely outside of physics, and so was your answer about the chemistry of egg boiling. That just needed to be said. :-) $\endgroup$ – CuriousOne Jan 26 '16 at 5:57
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An egg has to reach an inner temperature of 100C to cook and in water the egg shell is kept at 100C for five minutes in a heat bath.

Thus your question is answered by "can the egg shell be heated to 100C by the much hotter thin gas in the thermosphere"

In vacuum the egg will radiate away and go close to 0 kelvin, so in the thermosphere it will be a fight between outgoing radiation to incoming from the "heat bath". Well, the thermosphere does not provide a heat bath.

Although the thermosphere is considered part of Earth's atmosphere, the air density is so low in this layer that most of the thermosphere is what we normally think of as outer space.

So the answer is that the water from the egg will sublimate through its pores and the rest will be a solid at close to 0K .

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  • $\begingroup$ I already thought about it (see my first comment to the answer). The problem is, if egg would radiate heat faster than acquiring it, then why surrounding thin air doesn't do the same? $\endgroup$ – Dzmitry Lazerka Jan 26 '16 at 8:04
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    $\begingroup$ @DzmitryLazerka Thin gases do not radiate the same as dense as they have very few interactions, and it is interactions that give off black body . type radiation en.wikipedia.org/wiki/Thermosphere . Notice the gas is hot during the day when ultraviolet hits it. at night it cools. windows2universe.org/earth/Atmosphere/… $\endgroup$ – anna v Jan 26 '16 at 8:49
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    $\begingroup$ You are confusing energy with temperature. There are very few molecules per cm cube and have indivitual interactions with the ultraviolet, acquiring energy. The egg has many orders of magnitude more molecules than the equivalent volume of gas. The egg will be heated on one side and will be radiating on the other. It is a different question, not a heat bath question, whether the heat on the 10 cm^2 crossection of an egg from the sun radiation will cook it. $\endgroup$ – anna v Jan 26 '16 at 9:04
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    $\begingroup$ look at page 27 here tak2000.com/data/Satellite_TC.pdf / 5 c would not cook an egg $\endgroup$ – anna v Jan 26 '16 at 9:10
  • $\begingroup$ Thank you, looks that if I cover my egg with thin gold coating, my egg will actually cook (gold equilibrium is at 250°C at 100km altitude). $\endgroup$ – Dzmitry Lazerka Jan 26 '16 at 9:53
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EDIT : The egg I am considering doesn't have a shell

Temperature is a measure of the average kinetic energy of particles in a gas. In the thermosphere, the highly energetic solar radiation collide with the (having very less pressure) air, and are thus given very high velocities and so have a high temperature. However, the temperature shouldn't play a big role, especially since the air's pressure is so less.

Since the air pressure is lower, the boiling point of water decreases. Therefore the water inside the egg will just boil out in a short time before the high temperature outside can cook it. So what will remain is the remains of an egg without water and the egg would be at the same temperature as before. The conventional cooking of an egg is more complex, with heat coagulating up the proteins (and therefore the taste ?), the water getting heated up side by side all along gradually. Here the water gets boiled up instantaneously without changing the temperature, and what is left are the remains. The protein denaturization process here will be totally different and so even if the egg manages to get heated up to a high temperature (addressed below), it won't be cooked as you would have expected.

Secondly, the heating process will be totally different. In conventional cooking there are a number of molecules hitting the egg with small velocities while here there will be less number of molecules with extremely large velocities. Therefore the egg will not get uniformly boiled up, but get sparsely collided with molecules of air as well as from solar radiation, whose action might cause the egg to burn up in spots rather than getting cooked up. In short, there is nothing simpler than to put you egg in a cooker. Tossing it up to get fried is not a feasible option in my opinion. :P

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  • $\begingroup$ If the egg boils inside, it will explode. Even if it doesn't boil, the pressure differential would probably accomplish the same thing. For a simulation, put an uncracked raw egg in a microwave oven. $\endgroup$ – WGroleau Jan 26 '16 at 6:03
  • $\begingroup$ @WGroleau by egg i meant without a shell. with shell on there aren't too many interesting dynamics. $\endgroup$ – Bruce Lee Jan 26 '16 at 6:08
  • $\begingroup$ The egg has pores and the water would still evaporate; have you noticed how the bubble of air grows with the age of the egg? I know because in Greece for Easter we boil eggs and paint them red, 40 or 50. The market does not carry so many fressh eggs. Many of them might even be two weeks old. The bubble is important when the eggs collide in the custom of hitting the egg of the other and saying "Christ is risen". The goal is to keep your egg intact and the location of the air bubble is important. fractalart.gr/stis-rizes-tou-ethimou-1 $\endgroup$ – anna v Jan 26 '16 at 6:16
  • $\begingroup$ @annav my egg doesn't have a shell.. i have posted the edit now. and you are right in that the water would evaporate if it has pores on its shell. $\endgroup$ – Bruce Lee Jan 26 '16 at 6:23
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    $\begingroup$ @DzmitryLazerka nope it won't at all..as pointed out in a comment, the temperature experienced by a thermometer will be different than that is there in the thermosphere. Even if some very fast moving gas molecule in the thermosphere hits your dumbbell and melts a small part of it, then the molten part will quickly solidify by the virtue of blackbody radiation before another molecule can hit it. This is due to the less density of gas molecules. So it won't melt. $\endgroup$ – Bruce Lee Jan 26 '16 at 8:59

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