Biomes, occupying the surface Layer (and sometimes the subsurface layer as well) are the environment of a planet. Each biome determines what the surface will look like in their area, how many hills and mountains can generate, what plants will grow there, if any, and the weather and temperature.
Which Biomes Can Appear on a Planet?
Planets are defined by Major Biomes and each planet has a Dominant Biome (also referred to as the Primary Biome) - this biome is the one you see on the navigation console when first looking at a planet in your ship. The Dominant Biome defines the planet overall, including the background details, decides which Dungeons and Villages can spawn on that world and what other Major Biomes can be generated. Some Dominant Biomes do not allow any other biomes to appear. An example of this is the Arctic biome - when it is the dominant biome, no other biomes can appear on the surface or in the subsurface of the planet (the subsurface is occupied by the Arctic ocean floor).
Major Biomes have the most impact on the overall makeup of each planet: each has their own unique features and monsters, although not all creature spawns are determined by the biomes available; some are random. Planets can have several Major Biomes so long as the Dominant Biome lets them appear - the larger a planet is, the more Major Biomes it is likely to have. Major Biomes that are not Dominant are also known as Secondary Biomes.
All Major Biomes can also have Minor Biomes associated with them, also known as Mini-Biomes. Minor Biomes have unique characteristics to add diversity to the planets and frequently have their own unique treasure and items to find as well. If a Major Biome is present on a planet, any Minor Biome dependent on that Major Biome could appear on that world, even if that biome is not normally generated by the Dominant Biome. However, the biome has to be the Dominant one to allow the appearance of other Major Biomes.
This allows for a very wide variety of possible environments on different planets, and also means that you can find sometimes find features of low-Tier worlds on high-Tier worlds and vice versa - Garden biomes are occasionally found on Volcanic worlds, for example, which allows Volcanic worlds to sometimes have Spring biomes when they cannot do this normally.
These biomes are the possible Dominant Biomes of a generated planet. The temperature, enemies, additional biomes and weather of a planet are dependent on the biome reported in your navigation console on your ship.
Depending on the size of the planet, it can have several Major Biomes, if this is allowed on this particular planet type.
The Unknown threat level is meant to be ambiguous, in that no threat exists whatsoever until you acquire Erchius Fuel or bring some with you. It is actually registered in the game files as Tier 1 but does not strictly fit any Tier classification beyond this technicality.
As The Ruin is a custom boss encounter planet, it does not have a defined Tier at all.
These Mini-Biomes cannot be the dominant biome of a planet. Instead, these smaller biomes are generated within one of a planet's Major Biomes. These environments can have unique characteristics such as plants, monsters and blocks that are distinct from the main biome and are unique to that specific area.
|GIANT FLOWERS||HIVE||MUSHROOM PATCH|
Underground Caves are smaller biomes which can be found below the surface of a planet in place of a generic underground Layer. These environments can have unique characteristics such as plants, monsters and blocks that are distinct from the main biome, unique to that specific area. They can vary greatly from the biomes on that planet's surface, allowing you to discover materials that would otherwise be impossible to find there. All of these biomes may generate on any planet type except Moon, Barren, and Tentacle.
(The game will often refer to cave biomes as "<name> Caves", mainly to distinguish them from any similar surface biomes.)
|LUMINOUS CAVES||BONE CAVES||CELL CAVES|
|FLESH CAVES||ICE CAVES||MINI VILLAGE|
|MUSHROOMS||SLIME CAVES||STONE CAVES|
This Underground Cave is not found normally in the universe and exists only as part of The Ruin boss encounter.
|BRAIN (THE RUIN'S BRAIN)|