Official rule text
9.4 Abilities can cause a system tile to become an anomaly; that a The attached card maintains its exhausted or readied state. system tile is an anomaly in addition to its other properties. b If a planet card is purged, also purge all cards that are
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Source: Twilight Imperium: Fourth Edition - Living Rules Reference: Prophecy of Kings
Expansion: Prophecy of Kings
Version: 2.0
Reference: Rule 9.4