A quick and easy one for today. Have you watched Man of Steel? I’d rather (better) not comment on the movie itself, but we can probably agree than Zach Snyder was going for visually striking all through the film. Hence, there’re flying scenes everywhere where he shows how Superman breaks the sonic barrier and … kaboom, here’s a trail of white smoke on his tail like in jet planes!
Whether it is cool or not, is it scientifically sound that a flying man (go figure) can generate that trail?
In fact, jets do generate that white smoke because their engine exhaust mixes with the much cooler atmosphere, like when we exhale white poofs under very cold weather. In order to condense into clouds, the water vapor released by the jet needs the chemicals in the exhaust, including carbon dioxide, oxides of sulfur and nitrogen, unburned fuel, soot and metal particles, although other particles present in the air (if any, at those heights) can also help. All the mix in the contrail rotates with respect to the surrounding air and, voila, here comes the trail!
In brief: it Superman leaves a contrail during his flight he needs to: i) throw heat into the atmosphere; and ii) release a mix of chemicals and a large amount of water vapor. I, for one, do not wanna go there 😀
On a side note, it is interesting to note that the shape and duration of contrails may be used as weather indicator, since they feed on air humidity: a thick, lasting one might well predict a coming storm.
Leaving the chemicals sky spread aside, it’s been suggested that contrails might contribute to global warming because they behave like an insulating layer of moisture and gases in the atmosphere. More information in PhysOrg and Wired.