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I'm writing a speculative fiction story that includes superhumans, and I'm trying to get some of the specifics nailed down. Several of my superhumans have the typical powers of flight, usually able to break the sound barrier but not exceeding Mach 5. They'll fly everywhere from ground level to about 10 km above the ground.

I'm trying to determine if they'll leave a contrail behind them as they fly through the atmosphere. From my preliminary research on contrails (thank you, Wikipedia) I've learned that these are produced by either the condensation of warm CO2 and H2O or by pressure changes. My superhumans don't use combustion to fly, so it seems like the only way contrails could form would be via pressure differentials created by flying at supersonic speeds.

Would a superhuman flying through the air leave a contrail behind? If so, would it be permanent or under what conditions (speed, altitude) would this occur?

Edit: This question is specifically about the movement of a (human) body through the atmosphere under the defined circumstances, not how such movement might occur or the ramifications of such movement on clothes etc.

Bounty edit: I'm offering a bounty because the current answers, while helpful, don't provide actual estimates for the environmental conditions and velocities required to create a contrail. I'm aware that it's possible to create a contrail by passing a body through air fast enough under the right conditions, but my question is whether a Mach 5 superhuman would do so near ground level and in the mid-troposphere.

Bounty award I’m giving the bounty to Slipoch, but not the green check mark. If somebody’s able to answer the question and provide estimates of the speeds and environmental conditions required, I’ll contribute a larger bounty for an exemplary answer.

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Contrails are not produced by exhaust (aided in creation but not created by), as mentioned in my comment on the answer below. This is a pretty common misconception, which led to the rise of the idea of chemtrails.

You can see contrails on WW1 aeroplanes, and other non-jet propulsion based aircraft (such as twin & quad prop planes). How would that work if you assume a jet engine produces them? Jet engine exhaust does have a high water content, so it would aid the formation of contrails in the lower pressure area left behind.

They are actually produced by the condensation of air containing water in the lower pressure behind the wing tips, this is why even 4 jet engine planes often only leave 2 trails, it is all dependant on pressure and humidity at the altitude as well as any excess water vapour from the jet engine.

So yes, as long as the shape of the object moving fast enough is the right shape to create low enough pressure in it's wake and the water content of the surrounding air is high enough, then it can create a contrail.

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  • $\begingroup$ good answer, though anything moving through the atmosphere inherently creates pressure differentials in its wake. Except maybe for something like tear drop shaped. $\endgroup$ – anon Nov 13 '18 at 12:08
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    $\begingroup$ Hi Slipoch, thanks for the answer! Do you have any idea what ballpark those numbers (mostly speed) are in? I’m aware that if things move fast through the atmosphere, they’ll have contrails. I’m trying to figure out if Mach 1 and a human shape will leave behind a contrail. $\endgroup$ – Dubukay Nov 13 '18 at 23:09
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    $\begingroup$ What would be the right shape? Would it help if the superhuman were flying in a T-pose (assuming not wings)? With both arms stretched forward? The Superman (1 arm forward like he's punching the air)? Head first with arms at their sides? $\endgroup$ – miltonaut Nov 19 '18 at 14:54
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    $\begingroup$ I have one particular bone to pick with this answer, that being that you do see 4 contrails form behind a 4 engine aircraft. $\endgroup$ – Separatrix Nov 19 '18 at 15:00
  • $\begingroup$ Hi Dubukay, sorry man, it would depend on too many factors such as the water content at that altitude, air pressure, speed and shape of the body etc. $\endgroup$ – Slipoch Nov 20 '18 at 7:55
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You don't need to go as fast as Mach 5 and at high altitude. Contrails, or vapour trails can be produced at low altitude and relatively slow speeds: the following photo shows trails coming from the propeller tips of an aircraft on the ground: enter image description here

And here produced by a race car:

enter image description here

And before it's pointed out these are caused by a lift (or downforce) generating surface, here's a photo of a contrail produced by a bullet:

enter image description here

If you have the right conditions, namely a decent level of humidity, something going fast enough generating turbulence behind it, such as a flying human, could generate contrail.

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Meteor contrails seem to be a thing. I haven't been able to find any data on the velocities involved, but I would assume they are high.

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    $\begingroup$ Meteors are actively burning in the atmosphere $\endgroup$ – anon Nov 13 '18 at 12:05
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Yes and no. They would not leave them in general. Only when they go fast and do sharp turns in humid air, need to note this trails will be small compared to trails of engines.

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  • $\begingroup$ Maybe their flying superpower comes with supersweating, so they make the air around them very humid by just flying through it. $\endgroup$ – celtschk Nov 21 '18 at 18:16
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I don't think humans can leave aerodynamic contrails because nothing on the human body resembles the wings of an airplane, which are designed to create pressure differentials. Our heads are rounded, our limbs are like cylinders, and even our Air Jordans lack large planar surfaces. If a flying superhuman were to extend sword blades in his arms, like Deadpool, then perhaps contrails would form.

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  • $\begingroup$ You know what might create a pressure differential? A large non-aerodynamic solid object moving through air faster than the speed of sound - you'll get high-pressure air bleeding off the front, and a partial vacuum directly behind since there will be no tapering to help reintegrate the vortices in the wake. $\endgroup$ – Chronocidal Dec 11 '18 at 19:03
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No, because contrails are are line-shaped clouds produced by aircraft engine exhaust or changes in air pressure, typically at aircraft cruise altitudes several miles above the Earth's surface. Contrails are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures that exist at high altitudes allows the formation of the trails. Impurities in the engine exhaust from the fuel, including sulfur compounds (0.05% by weight in jet fuel) provide some of the particles that can serve as sites for water droplet growth in the exhaust and, if water droplets form, they might freeze to form ice particles that compose a contrail. Their formation can also be triggered by changes in air pressure in wingtip vortices or in the air over the entire wing surface. Contrails, and other clouds directly resulting from human activity, are collectively named homogenitus. Since were no jets we would not produce contrails

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    $\begingroup$ Hi Nomad, I’ve already read the Wikipedia page it looks like you copy-pasted (most of) this answer from, and I’m hoping to discuss the pressure differentials side of things. Just because we aren’t jets doesn’t mean we can’t produce contrails. $\endgroup$ – Dubukay Nov 13 '18 at 0:44
  • $\begingroup$ @Dubukay, while not as complete as I would have hoped, Nomad isn't wrong. The jet engines are creating a point of high pressure and high temperature behind the engine. The formation of the cloud is basic physics (I remember a great episode of Laverne & Shirley where Shirley declared that the open door separating their overheated apartment and overcold hall should have rain). Superman, on the other hand, is not generating heat at all (other than by compression, which is insufficient) and actually creates a vacuum (low pressure) behind him. No contrail. $\endgroup$ – JBH Nov 13 '18 at 0:51
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    $\begingroup$ Nomad, we actually like quoting sources, but you should quote them rather than plagarizing them. Use the ">" character at the beginning of a line to start a quotation and always provide a link to the source. I'll be happy to upvote your answer if you reformat to provide the quote and a source link. $\endgroup$ – JBH Nov 13 '18 at 0:52
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    $\begingroup$ Contrails are not produced by exhaust, you can see contrails on WW1 aeroplanes. How would that work if you assume a jet engine produces them? they are actually produced by the trail usually left by the condensation of air in the 'gap' or lower pressure behind the wing tips, this is why even 4 jet engine planes only leave 2 trails. $\endgroup$ – Slipoch Nov 13 '18 at 3:30

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