There are seven normal and six hostile planet types. The various hostile types require increasingly advanced technology to colonize. Size determines the planet's initial population capacity. Mineral wealth dramatically influences a colony's industrial productivity while Habitability influences population growth rates. Hostile planets are the most likely to be rich or ultra-rich in minerals. Artifact worlds contain relics of a now-vanished advanced civilization. All planets can be upgraded to Gaia class with the appropriate technologies. Planets can be upgraded in three ways: