Entropy · Board game rules
Does a star prevent other placements?
Quick answer
A Star only blocks the placement of another Star in the same Solar System — it does not prevent Planets or Asteroids from being placed there.
Details
When resolving Evolve a Star, you may pay 1 Energy to add a tier I Star tile only to a Solar System that has no Star tile yet, or to a brand-new Solar System [p.7 — Evolve a Star]. This means a Solar System can only ever contain one Star, so an existing Star effectively prevents another Star from being added to that same system.
Aside from this, Stars have no bearing on placing Planets (which go into empty Planet spaces of a Solar System via Aggregate Planet) [p.8 — Aggregate Planet] or Asteroids (which are placed on empty spaces of a Planet, up to 2 per Planet) [p.11 — Catch an Asteroid]. Stars instead contribute to Life Conditions and provide activatable effects, but they don't occupy or block Planet/Asteroid spaces.
Watch out: If you want to upgrade a Star to the next tier, you must exchange the existing Star for the next one in the same Solar System — this is different from adding a brand-new tier I Star, which requires an empty Star slot [p.7 — Evolve a Star].