diff --git a/BuildController.gd b/BuildController.gd
index f316929..02fb933 100644
--- a/BuildController.gd
+++ b/BuildController.gd
@@ -543,10 +543,13 @@ func _refresh_build_status() -> void:
 
 	# Prices are shown under each option now, so this only needs to say
 	# whether the fleet is somewhere an extractor could go.
-	if _planet_under_fleet() != null:
-		build_status.text = "Over %s - an extractor can be built here" % _planet_under_fleet().planet_name
-	else:
+	var planet: Node2D = _planet_under_fleet()
+	if planet == null:
 		build_status.text = ""
+	elif not GameState.is_planet_conquered(planet.planet_id):
+		build_status.text = "Over %s - capture it before building an extractor" % planet.planet_name
+	else:
+		build_status.text = "Over %s - an extractor can be built here" % planet.planet_name
 
 
 func _refresh_build_option_states() -> void:
@@ -554,7 +557,8 @@ func _refresh_build_option_states() -> void:
 		var definition: Resource = entry[4]
 		var enabled: bool = GameState.is_building_unlocked(definition.definition_id)
 		if definition.placement_mode == "planet":
-			enabled = enabled and _planet_under_fleet() != null
+			var planet: Node2D = _planet_under_fleet()
+			enabled = enabled and planet != null and GameState.is_planet_conquered(planet.planet_id)
 		entry[1].enabled = enabled
 		entry[1].queue_redraw()
 
@@ -593,6 +597,9 @@ func _show_building_info(type: String) -> void:
 		if planet == null:
 			lines.append("No planet in reach - fly over one.")
 			can_build = false
+		elif not GameState.is_planet_conquered(planet.planet_id):
+			lines.append("%s is not captured yet - take all its capture points." % planet.planet_name)
+			can_build = false
 		elif GameState.has_extractor_at(planet.planet_id):
 			lines.append("%s already has an extractor." % planet.planet_name)
 			can_build = false
@@ -639,6 +646,9 @@ func _confirm_build() -> void:
 		if planet == null or GameState.has_extractor_at(planet.planet_id):
 			build_status.text = "No planet in reach any more"
 			return
+		if not GameState.is_planet_conquered(planet.planet_id):
+			build_status.text = "%s is not captured yet" % planet.planet_name
+			return
 		if not GameState.spend(definition.cost):
 			build_status.text = "Not enough rocks (need %d, have %d)" % [definition.cost, GameState.rocks]
 			return
diff --git a/GameState.gd b/GameState.gd
index 3854f56..0f2a3db 100644
--- a/GameState.gd
+++ b/GameState.gd
@@ -1020,6 +1020,66 @@ func _extractor_inventory(extractor: Dictionary) -> RefCounted:
 	return inventory
 
 
+# Planet conquest: a planet must have every one of its capture points held
+# before an extractor can be built there (see BuildController's placement
+# gates). Keyed by the same stable planet_id as `extractors`, entirely
+# separate from it - a planet can be conquered long before anyone builds an
+# extractor on it, or never get one at all.
+var planet_capture: Dictionary = {}
+
+signal planet_conquered(planet_id: String)
+
+
+func register_capture_points(planet_key: String, total: int) -> void:
+	# Idempotent: landing again on a planet must not wipe points already
+	# captured on a previous visit.
+	if planet_capture.has(planet_key):
+		return
+	var captured: Array = []
+	captured.resize(total)
+	captured.fill(false)
+	planet_capture[planet_key] = {"captured": captured, "conquered": false}
+
+
+func capture_state(planet_key: String) -> Dictionary:
+	return planet_capture.get(planet_key, {"captured": [], "conquered": false})
+
+
+func is_point_captured(planet_key: String, index: int) -> bool:
+	var captured: Array = capture_state(planet_key).get("captured", [])
+	if index < 0 or index >= captured.size():
+		return false
+	return bool(captured[index])
+
+
+func mark_point_captured(planet_key: String, index: int) -> void:
+	if not planet_capture.has(planet_key):
+		return
+	var state: Dictionary = planet_capture[planet_key]
+	var captured: Array = state.captured
+	if index < 0 or index >= captured.size():
+		return
+	captured[index] = true
+	if state.conquered:
+		return
+	if captured.all(func(c): return bool(c)):
+		state.conquered = true
+		planet_conquered.emit(planet_key)
+
+
+func is_planet_conquered(planet_key: String) -> bool:
+	return bool(capture_state(planet_key).get("conquered", false))
+
+
+func captured_point_count(planet_key: String) -> int:
+	var captured: Array = capture_state(planet_key).get("captured", [])
+	var count: int = 0
+	for c in captured:
+		if c:
+			count += 1
+	return count
+
+
 func _process(delta: float) -> void:
 	# Runs in the autoload, so mining and transport continue while the player
 	# is on a planet's surface or nowhere near either.
diff --git a/tests/test_extractor_building.gd b/tests/test_extractor_building.gd
index 0e52c21..656c2c5 100644
--- a/tests/test_extractor_building.gd
+++ b/tests/test_extractor_building.gd
@@ -42,6 +42,12 @@ func _initialize() -> void:
 	game_state.rocks = 200
 	game_state.buildings.clear()
 	game_state.extractors.clear()
+	game_state.planet_capture.clear()
+	# This test is about the planet-proximity/duplicate rules, not conquest
+	# (see test_planet_conquest_gate), so pre-conquer the target planet.
+	var target_planet_id: String = "chunk:%d:%d" % [target_chunk.x, target_chunk.y]
+	game_state.register_capture_points(target_planet_id, 1)
+	game_state.mark_point_captured(target_planet_id, 0)
 	# Extractors are gated behind research (see test_skill_tree). This test
 	# is about the planet-proximity rule, so grant the research up front.
 	game_state.reset_progression()
diff --git a/tests/test_planet_conquest_gate.gd b/tests/test_planet_conquest_gate.gd
new file mode 100644
index 0000000..93b69ba
--- /dev/null
+++ b/tests/test_planet_conquest_gate.gd
@@ -0,0 +1,157 @@
+extends SceneTree
+
+# Headless gameplay test: run with
+#   godot --headless -s res://tests/test_planet_conquest_gate.gd
+# Verifies:
+#   1. GameState starts every planet unconquered, and register_capture_points
+#      is idempotent (a second call with the same total doesn't wipe progress)
+#   2. mark_point_captured only conquers once every point is captured, and
+#      the planet_conquered signal fires exactly once
+#   3. over an unconquered planet, the extractor build option is disabled,
+#      the info popup explains why, and confirming spends nothing and builds
+#      nothing
+#   4. once conquered, the same build flow works and charges the cost
+
+var main_scene: Node
+var fleet: Node
+var game_state: Node
+var controller: Node
+var button: IconButton
+var popup: Control
+var target_chunk: Vector2i
+var stage: int = 0
+var elapsed: float = 0.0
+var conquered_signal_count: int = 0
+
+
+func _initialize() -> void:
+	var found: bool = false
+	for x in range(-15, 15):
+		for y in range(-15, 15):
+			var chunk: Vector2i = Vector2i(x, y)
+			if WorldGen.has_planet_at_chunk(chunk):
+				target_chunk = chunk
+				found = true
+				break
+		if found:
+			break
+	if not found:
+		return _fail("no planet chunk to test with")
+
+	game_state = root.get_node("GameState")
+	game_state.rocks = 200
+	game_state.buildings.clear()
+	game_state.extractors.clear()
+	game_state.planet_capture.clear()
+	game_state.reset_progression()
+	for node in GameState.SKILL_TREE:
+		game_state.unlocked.append(node.id)
+
+	var target_planet_id: String = "chunk:%d:%d" % [target_chunk.x, target_chunk.y]
+
+	# Unit-level checks on GameState itself, before any scene involvement.
+	if game_state.is_planet_conquered(target_planet_id):
+		return _fail("a fresh planet reported conquered")
+	game_state.register_capture_points(target_planet_id, 3)
+	game_state.mark_point_captured(target_planet_id, 0)
+	game_state.register_capture_points(target_planet_id, 3)   # idempotent re-registration
+	if game_state.captured_point_count(target_planet_id) != 1:
+		return _fail("re-registering wiped already-captured progress")
+	game_state.planet_conquered.connect(func(_id): conquered_signal_count += 1)
+	game_state.mark_point_captured(target_planet_id, 1)
+	if game_state.is_planet_conquered(target_planet_id):
+		return _fail("conquered with points still missing")
+	game_state.mark_point_captured(target_planet_id, 2)
+	if not game_state.is_planet_conquered(target_planet_id):
+		return _fail("all points captured but planet not marked conquered")
+	# Marking an already-captured point again must not double-fire the signal.
+	game_state.mark_point_captured(target_planet_id, 2)
+	if conquered_signal_count != 1:
+		return _fail("planet_conquered fired %d times, expected exactly 1" % conquered_signal_count)
+
+	# Reset conquest for the scene-level gate check below - this run tests
+	# the unconquered path first, then conquers it.
+	game_state.planet_capture.clear()
+
+	main_scene = load("res://Main.tscn").instantiate()
+	root.add_child(main_scene)
+	fleet = main_scene.get_node("Fleet")
+	controller = main_scene.get_node("BuildController")
+	button = main_scene.get_node("UI/BuildMenu/ExtractorButton")
+	popup = main_scene.get_node("UI/BuildMenu/InfoPopup")
+
+
+func _process(delta: float) -> bool:
+	elapsed += delta
+	match stage:
+		0:
+			main_scene.get_node("AsteroidField").set_process(false)
+			main_scene.get_node("EnemySpawner").set_process(false)
+			var near: Vector2 = WorldGen.chunk_origin(target_chunk) + Vector2.ONE * WorldGen.CHUNK_SIZE * 0.5
+			for ship in fleet.ships:
+				ship.position = near
+			fleet.move_to(near)
+			elapsed = 0.0
+			stage = 1
+			return false
+		1:
+			var planet_field: Node = main_scene.get_node("PlanetField")
+			if elapsed < planet_field.check_interval + 0.2:
+				return false
+			if not planet_field.populated_chunks.has(target_chunk):
+				return _fail("planet never spawned")
+			var planet: Node2D = planet_field.populated_chunks[target_chunk][0]
+			for ship in fleet.ships:
+				ship.position = planet.position
+			fleet.move_to(planet.position)
+			elapsed = 0.0
+			stage = 2
+			return false
+		2:
+			if elapsed < 0.3:
+				return false
+			var planet_field: Node = main_scene.get_node("PlanetField")
+			var planet: Node2D = planet_field.populated_chunks[target_chunk][0]
+
+			controller._on_build_pressed()
+			if button.enabled:
+				return _fail("extractor option enabled over an unconquered planet")
+			controller._show_building_info(GameState.BUILDING_EXTRACTOR)
+			var explains_capture: bool = popup.visible \
+				and "captur" in popup.get_node("Panel/MessageLabel").text.to_lower()
+			var offered: bool = popup.get_node("Panel/BuildButton").visible
+			if not explains_capture or offered:
+				return _fail("unconquered popup did not explain itself, or offered a build")
+			var rocks_before: int = game_state.rocks
+			controller._confirm_build()   # must do nothing even if somehow pressed
+			if game_state.rocks != rocks_before or not game_state.extractors.is_empty():
+				return _fail("build proceeded over an unconquered planet")
+			popup.visible = false
+
+			# Now conquer it and confirm the same flow succeeds.
+			game_state.register_capture_points(planet.planet_id, 2)
+			game_state.mark_point_captured(planet.planet_id, 0)
+			game_state.mark_point_captured(planet.planet_id, 1)
+
+			controller._on_build_pressed()
+			if not button.enabled:
+				return _fail("extractor option stayed disabled after conquest")
+			controller._show_building_info(GameState.BUILDING_EXTRACTOR)
+			if not popup.get_node("Panel/BuildButton").visible:
+				return _fail("conquered planet did not offer a build")
+			controller._confirm_build()
+			var built: bool = game_state.has_extractor_at(planet.planet_id)
+			var charged: bool = game_state.rocks == rocks_before - GameState.EXTRACTOR_COST
+			if not built or not charged:
+				return _fail("conquered planet did not build/charge correctly")
+
+			print("TEST_PLANET_CONQUEST_GATE: PASS")
+			quit(0)
+			return true
+	return false
+
+
+func _fail(message: String) -> bool:
+	print("TEST_PLANET_CONQUEST_GATE: FAIL (%s)" % message)
+	quit(1)
+	return true
diff --git a/tests/test_planet_conquest_gate.gd.uid b/tests/test_planet_conquest_gate.gd.uid
new file mode 100644
index 0000000..236fedc
--- /dev/null
+++ b/tests/test_planet_conquest_gate.gd.uid
@@ -0,0 +1 @@
+uid://k4l7u3r84jch