Official rule text
Some of these abilities are followed by a second number PLANET TRAITS presented inside parentheses. This number indicates how many Most planets outside of home systems have a planet trait. dice a player rolls. There are three types of planets: cultural, hazardous, and For example, when a player uses an ability that reads “Space industrial. Traits have no inherent game effect, but are referred Cannon 5 (x3),” they roll three dice and each die with a result of to by some cards and abilities. “5” or higher produces one hit. If an ability that requires a roll does not contain a number inside parentheses, a player only rolls one die.
View official source
Source: Twilight Imperium: Fourth Edition - Rules
Expansion: Base Game
Version: source text