Category-3 planet

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A category 3 planet has a complete ecosystem with 3 shrubs, 3 bushes, 3 trees, 6 herbivores, and 3 carnivores or omnivores. A T-3's atmospheric level and temperature are optimal for hosting life. In summary, T-3 worlds are generally the greenest planets with minimal amounts of bare terrain and swathes of forests, alongside an abundance of fauna. There are a few unclaimed T-3 planets around, insufficient to make it worth your while searching for them, and a good quantity of them bear the remains of tribes and civilisations long passed.

[edit] T-3 planets and your empire

A T-3 planet can support 3 colonies each with no "bubble" to hold in air and the maximum number of buildings, including turrets. The exception to this are homeworlds which can have more than three colonies, most but not all home planets are T-3. T-3 planets are very important to your empire as they can create spice faster and in larger quantities than any other level of planet, (except T-2 Planets with no turrets, however they have less cities) especially captured homeworlds with more than 5 cities.