I recently re-watched the film Serenity and noticed an odd scene two thirds of the way through the film. After deciding to disguise the spaceship Serenity with intact human bodies, the ship is shown taking off. As it climbs out of the atmosphere the bodies are burning and all that is left are the skeletons. Spacecraft do not tend to experience flame around the hull due to atmospheric friction on take off. My question is was this a plot point for the film, does it have an in universe explanation, or was it simply rule of cool on behalf of the special effects team? Thank you.
The actual answer is that it is entirely possible/likely that what is depicted in Serenity in that scene is what would happen in real life.
As Valorum mentioned in his comment, there is information here on atmospheric heating when entering an atmosphere at high speed, quoted:
The term "friction" is a misnomer. The source of heat is adiabatic compression - gas on trajectory of the reentering object is compressed against its leading surface, and as result heats up.
Due to inertia of the gas, it takes some time before it moves sideways off the leading surface (giving away some of its heat to the object it touches at the time), and flies free off the edges, the following decompression (and resulting cooling) occurring far beyond the surface of the object, and so unable to cool it back down. There's also an adiabatic decompression on the trailing side, which would cool it down - except while the pressure there can drop only by 1 bar (from atmospheric to zero) the pressure can rise much more on the leading side, causing much more heating than cooling effect on the object.
As we know from studies related to the SR-71 "Blackbird" hypersonic aircraft, atmospheric heating is caused by traveling through the atmosphere at high speed in any direction (the SR-71 never left or re-entered the atmosphere), and the temperatures reached can be high (emphasis added):
The resulting data helped improve theoretical prediction methods and computer models dealing with structural loads, materials, and heat distribution at up to 800 °F [427 °C], the surface temperatures reached during sustained speeds of Mach 3.
Above 1500 °C or so, human bones will burn to ash and disintegrate (which does not happen in the movie), so all that needs to be true for the Serenity scenario to actually happen is for Serenity (the ship, not the movie) to travel through the atmosphere somewhere above Mach 3 but not so fast that the heating causes temperatures above 1500 °C. Assuming a fictional propulsion source of unknown specific capabilities but certainly with ability to reach escape velocity very quickly, this seems completely possible.