In the Galaxy, there are a few planets known as Crater Planets scattered around. These planets are typically Rocky Planets or Flurry Planets, although it may sometimes be another type of planet. They have rough surfaces, and Habitable Planets and Water Planets will have these filled up with water, such as the T1 Planet in your first Mission. When these planets have extra water, they will often become impossible to colonise without the use of terra-sculpting tools. One example of a Crater planet is The Moon, though there are many other Crater planets that can be in Star systems. Unlike their real counterparts, Mercury and Mars are not Crater Planets like the Moon.