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Contrails, as far as I understand them, are caused by either a pressure change that forces the condensation of H2O(g) OR by the release of warm H2O from a combustion engine. Most plane contrails, I would assume, operate largely by this second mechanism as they burn jet fuel and release warm CO2 and H2O.

My question is, can the first mechanism alone be enough to create a contrail? Would a supersonic object passing through Earth's atmosphere leave behind a contrail? If so, what conditions are required for this - presumably high pressure (close to the surface of the Earth) and high speed?


For those curious, this started out as a question on Worldbuilding and has been asked again here per a wise comment.

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The space shuttle is an example of the phenomenon of a supersonic craft leaving behind a contrail.

The Fact that the space shuttle flies as a glider on re-entry is stated by NASA here.

The velocity of the space shuttle at different altitudes during descent is depicted here in the section "Repeat explanation of a Shuttle reentry and landing".

The space shuttle leaving behind a contrail is shown in the third space shuttle image on this page, and by an enthusiast here.

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The Chelyabinsk meteor left a contrail (https://www.nature.com/news/russian-meteor-largest-in-a-century-1.12438) although it was not reported to carry engines:-)

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  • $\begingroup$ But meteors are actively igniting things due to the heat generated by the shock wave compression during entry. So there is combustion in that example. $\endgroup$ – honeste_vivere Nov 28 '18 at 15:06
  • $\begingroup$ @honeste_vivere: What "things" are they "actively igniting"? Air cannot be "ignited", and, judging by the composition of the meteor (researchgate.net/publication/…), it does not seem to contain significant amount of "fuel" that can cause exothermic reaction with air. So I am not sure about combustion, but there was no "combustion power source". $\endgroup$ – akhmeteli Nov 28 '18 at 15:22
  • $\begingroup$ The oxidation of iron is exothermic and with the constant heat source of the compressed air behind the shock wave heating the iron, it can continue to combust (yes iron). This can be done with acetylene torches when cutting through iron. Once you start cutting, you can actually shut off the acetylene. There are lots of other materials on meteors that are combustable at lower temperatures than iron. If not combustion, what do you propose explains the trail of fire-like emission from meteors? $\endgroup$ – honeste_vivere Nov 28 '18 at 15:33
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    $\begingroup$ @honeste_vivere : Your remark on oxidation of iron being exothermic is correct but irrelevant, as there was no iron in Chelyabinsk meteor, there was only an oxide of iron (please see the information on the meteor's composition at the link of my previous comment - there are indeed meteors containing a lot of metals, but this was not the case for this specific meteor). As for explanation of the trail, it is possible that ablated particles served as centers of condensation in oversaturated air. $\endgroup$ – akhmeteli Nov 29 '18 at 3:23
  • $\begingroup$ I used iron just as a figurative example, not to be treated as the actual metal of the meteor. As for the ablation, how do you go through to the ablation stage of a metal before melting and/or combustion in an oxygenated environment? Isn't the energy needed to ablate higher than to combust or melt for most metals? $\endgroup$ – honeste_vivere Nov 29 '18 at 15:09

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