Entropy · Board game rules
Can lifeform tokens be placed on any planet?
Quick answer
No — Lifeform tokens are only added to a Planet when a Life card is successfully played there, and each Planet can hold a maximum of 5 Lifeforms of each type.
Details
Lifeform tokens are placed on a Planet as a result of the Create Life action: you play a Life card to a chosen Planet, but only if that Planet (and its Asteroids) together with the Star in its Solar System meet the card's Life Condition requirements (Heat, Carbon, Water, Radiation) [p.8 — Actions]. If those conditions aren't met, you cannot play the card there, so tokens cannot simply be placed on any Planet at will.
Once the conditions are satisfied, you add the indicated Lifeform tokens next to the Planet tile (the "Local" symbol) as part of resolving the card [p.8 — Actions]. However, each Planet is capped at a maximum of 5 Lifeforms of each type (Bacteria, Plant, Animal) [p.9 — Actions].
Other actions can also add or change Lifeforms on a Planet, such as the Traffic Bonus on Create Life (which adjusts the number gained) [p.9 — Actions], the Traffic Bonus on Primordial Soup (which lets you gain or advance Lifeforms on a Planet with fewer than 5 of that type) [p.11 — Actions], and certain Star or Focus card effects. All of these still respect the 5-per-type cap per Planet.
Watch out: Some Life cards also require you to remove existing Lifeform tokens from the chosen Planet as part of their requirement (shown by a red number) — this is a cost, not a placement [p.8 — Actions].