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What happens to the human body if blown out the airlock in space?
According to the Bioastronautics Data Book (http://adsabs.harvard.edu/abs/1973NASSP3006.....P), space death will occur something like this:
Some degree of consciousness will probably be retained for 9 to 11 seconds (see chapter 2 under Hypoxia). In rapid sequence thereafter, paralysis will be followed by generalized convulsions and paralysis once again. During this time, water vapor will form rapidly in the soft tissues and somewhat less rapidly in the venous blood. This evolution of water vapor will cause marked swelling of the body to perhaps twice its normal volume unless it is restrained by a pressure suit. (It has been demonstrated that a properly fitted elastic garment can entirely prevent ebullism at pressures as low as 15 mm Hg absolute [Webb, 1969, 1970].) Heart rate may rise initially, but will fall rapidly thereafter. Arterial blood pressure will also fall over a period of 30 to 60 seconds, while venous pressure rises due to distention of the venous system by gas and vapor. Venous pressure will meet or exceed arterial pressure within one minute. There will be virtually no effective circulation of blood. After an initial rush of gas from the lungs during decompression, gas and water vapor will continue to flow outward through the airways. This continual evaporation of water will cool the mouth and nose to near-freezing temperatures; the remainder of the body will also become cooled, but more slowly.
Since the Xenomorph is not a human body and there have been many instances you see the Xenomorph in zero atmosphere in Alien: Isolation, Alien: Covenant and in the EU. It's fair to assume that it would or could survive in space.
But since the Big Chap from Alien was also blasted by the thrusters of the Nostromo, until recently it was fair to assume it was dead. When Alien: Covenant came out in 2017 it challenged a lot of things which were cemented in canon for quite some time, and one of them was that the Xenomorph is succeptible to fire or extreme temperatures.
Even in Alien 3 the Alien survived being submerged into molten lead which is between 327.5 °C and 1,749 °C. It wasn't until the Xenomorph was also exposed to water did the beast shatter under extreme cooling.
So during the Cargo Lander fight scene with Daniels in Alien: Covenant, depending on what fuel mixture the Cargo Lander was using at the time of the fight scene would determine the resilliance of the Xenomorph.
It's also important to note that in the novelisation Daniels makes a point to T that the fuel mix must be strong enough to lift out of the planet's gravitational pull and reach the Covenant in orbit.
Rockets run with combustion temperatures that can reach ~3,500 K (~3,200 °C or ~5,800 °F)
Inside the typical commercial jet engine, the fuel burns in the combustion chamber at up to 2000 degrees Celsius. The temperature at which metals in this part of the engine start to melt is 1300 degrees Celsius, so advanced cooling techniques must be used.
The original Alien’s body was not destroyed by a thermal shock of over 6,200 °F/3426°C
I believe the Alien is dead because no trace of it could be found outside the ship when the lifeboat was recovered in Aliens.
And even if it did survive space there was no source of food for the Alien to survive, if it even needs a source of food once it is an adult.
In the early script and concept the Alien was in its last phase before dying, so even then if it were to survive in space or without food it would die according to its lifespan.
Unless you take the events in Alien Out of the Shadows, where the Alien was in hibernation for a very long time and only awoke in the presence of humans. Then the Alien is still out there.
The canon Xenomorph (currently under construction)
Interesting reading material at Strange Shapes about the Xenomorph from Alien.
According to Ridley Scott, he conceived the Alien as having a lifespan of only a few days — the reason it hides within the Narcissus and shows no real interest in attacking Ripley (until she provokes it) was because it was coming to the end of its life and was looking for a perfect place to die alone. - Paul Scanlon, Michael Gross. The Book of Alien, p. 87 (1979), Heavy Metal Press.
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