Factual error: During the Mars-flight, the way the spacecraft uses the rocket thrusters is unrealistic. For example when they are nearing Mars, they should be using the rockets against their movement, to slow down the speed. But in the movie they are using the rockets towards Mars.
Factual error: Crew members aboard the spaceship at the planet Mars are shown in instant communication with Earth. Because of the distance, a few minutes must pass each time before communication is made (between 10 and 22 minutes depending on where the planets are in their orbits, and that's each way so at least 20 minutes from when you say something until you hear what they say back).
Answer: Nothing would happen to them. The restriction on sexual activity was to keep them from spreading any potential contaminants through bodily fluids. It's nonsense because there are plenty of ways to spread bodily fluids that don't involve sexual contact and 10 days seems arbitrary, but it fits with the overall erotic themes of the film series to have the quarantine specify no sexual intercourse.
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