The Lonely - S1-E7
Factual error: Corey is in solitary confinement on an asteroid. However, asteroids are neither large enough nor stable enough to hold an atmosphere. In addition, the distance from earth stated in the episode wouldn't be much further than the moon; there are no asteroids in a stable, regular orbit around the the moon or the earth, nor around the sun anywhere that close to earth.
Answer: It's explained in the episode. The aliens are experimenting to see how humans react to various scenarios. This just happens to involve them using super strength.
Thanks. It's been a long time since I saw the episode so I forgot.