I'm not sure how to give a planet a trait, I replaced Habitable with BarrenWorld for Mars but that causes an error and game wont launch.
D:\Games\Steam\steamapps\common\Galactic Civilizations III/Data/Game\PlanetDefs.xml(25,34): error:
value 'BarrenWorld' not in enumeration
Are you saying I need to make a new planet trait? If so how do I make it affect Mars for example.