Other event notes

Pirates - The pirates don't have to be in one of your systems; they can be on the far side of the galaxy from you, and still impact your trade. Sometimes AI fleets will wipe out the pirates for you, if you are patient.

Accident - in the long run, ironically this can be one of the best events in the game. There is a mid-level Planetology tech that allows you to improve your planets' atmospheres, converting them from hostile to normal worlds. If you have access to that technology, and an accident occurs on one of your planets, it is frequently the case that the planet's size after the accident, cleanup, and re-terraforming is larger than the planet was originally.