 Ostensibly this is so that they can gain an understanding of the concept of "good vs. evil"

In the videogame StarCraft, the main hive world of the Zerg is located on Char, a planet with important volcanic activity.The surface is covered in ash while the underground is filled with lava.Before, and certainly after, the results sent back by the Viking landers, some science fiction set on Mars portrayed it as a desert planet.