This page describes events that randomly occur given enough time, but does not include pre-determined discoveries or planet events triggered by science ships, during exploration of star systems.
Colony Discoveries
Whether these events occur are determined based on whether a colonized world has a specific feature, but when they spawn is random and usually occurs within a few years after colonization. These events are not chains, and act as a single event. If a colony world has multiple features, multiple of these events should eventually occur.