Legend has it of the lost planet Anrakki, which was wiped from the universe by a remarkably improbable combination of planetary earthquakes, tsunamis, drought, famine and plague - all on the same day! -Old campfire story, “The Legend of Anrakki”
Planets may occasionally be affected by a significant event such as an outbreak of disease, global famine, or economic recession. The chances of such an event occurring often depend upon the characteristics of the planet and the nature of the activities carried out there - for example, a planet which sees a large amount of trading activity is more likely to experience an economic boom. As another example, a planet which has trade routes with another planet that is suffering from plague, is more likely to itself fall victim to an outbreak of plague. These planetary events will permanently affect one or more of the planetary characteristics, either increasing or decreasing the wealth or population, for example.
Watch out for planetary events on the galactic news ticker. You may want to alter your plans or take other action as a result of these events - particularly in the case of plague, which is rare, but can infect and even kill your dynasty members and retainers should it spread to your homeworld.
As seen in the Rulebook
The higher a planet's infrastructure budget, the greater the chance of an economic boom. The lower the planet's infrastructure budget, the greater the chance of an economic recession. Droughts and famines can be easily exploited by Mercantile and Agriculture houses.