Here are updated and clarified rules for mines in space combat:
Mines are fired during the Attack Phase of the space combat turn, using the Launch Mine action:
Launch Mine: Places a mine in the segment where the ship is located. Roll a normal attack roll and note down the result, which represents how well placed the mine is. No target lock is needed and the roll gets no penalty for this. Place any appropriate marker in the segment to mark where the mine is. When any other ship moves into the segment, the attack from the mine is immediately triggered, directly in the Pilot Phase of the turn. Countermeasures can be used against the mines, see Defensive Fire (this uses up the Gunner’s action for the turn however). The ship that launched the mine will not trigger it, nor will other ships already present in the segment. Note however that nuclear mines will damage all ships in the segment, and antimatter mines hit all ships within Short range.