diff --git a/BuildController.gd b/BuildController.gd
index 1d33801..ae3c914 100644
--- a/BuildController.gd
+++ b/BuildController.gd
@@ -563,7 +563,7 @@ func _show_building_info(type: String) -> void:
 		if planet == null:
 			lines.append("No planet in reach - fly over one.")
 			can_build = false
-		elif GameState.has_extractor_at(planet.planet_name):
+		elif GameState.has_extractor_at(planet.planet_id):
 			lines.append("%s already has an extractor." % planet.planet_name)
 			can_build = false
 		else:
@@ -606,13 +606,13 @@ func _confirm_build() -> void:
 
 	if definition.placement_mode == "planet":
 		var planet: Node2D = _planet_under_fleet()
-		if planet == null or GameState.has_extractor_at(planet.planet_name):
+		if planet == null or GameState.has_extractor_at(planet.planet_id):
 			build_status.text = "No planet in reach any more"
 			return
 		if not GameState.spend(definition.cost):
 			build_status.text = "Not enough rocks (need %d, have %d)" % [definition.cost, GameState.rocks]
 			return
-		GameState.add_extractor(planet.planet_name, planet.position, planet.resource_type)
+		GameState.add_extractor(planet.planet_name, planet.position, planet.resource_type, planet.planet_id)
 		build_menu.visible = false
 		return
 
diff --git a/GameState.gd b/GameState.gd
index 37d110a..b3d700b 100644
--- a/GameState.gd
+++ b/GameState.gd
@@ -18,6 +18,7 @@ var return_world_position: Vector2 = Vector2.ZERO
 var return_camera_zoom: float = 1.0
 
 var planet_name: String = ""
+var planet_id: String = ""
 var planet_definition_id: String = "rocky"
 
 # Explored-chunk history for the world map's fog-of-war reveal. Lives
@@ -881,15 +882,16 @@ func rotate_formation(radians: float) -> void:
 # Extractors mine into their OWN local stock. They do not own a magical
 # hauler: ore becomes spendable only when a hub-stationed transporter picks
 # up a full load and physically delivers it to the mothership. Entries are
-# {"position", "planet_name", "resource_type", "inventory", "mining_progress"}.
+# {"position", "planet_id", "planet_name", "resource_type", "inventory", "mining_progress"}.
 const EXTRACTOR_RATE: float = 2.0  # ore per second
 
 var extractors: Array = []
 
 
-func has_extractor_at(planet_name: String) -> bool:
+func has_extractor_at(planet_key: String) -> bool:
 	for e in extractors:
-		if e.planet_name == planet_name:
+		# Old saves have no planet_id; their name remains a migration fallback.
+		if String(e.get("planet_id", e.get("planet_name", ""))) == planet_key:
 			return true
 	return false
 
@@ -897,9 +899,12 @@ func has_extractor_at(planet_name: String) -> bool:
 signal extractor_added(planet_name: String)
 
 
-func add_extractor(planet_name: String, at_position: Vector2, resource_type: String = "ore") -> void:
+func add_extractor(planet_name: String, at_position: Vector2, resource_type: String = "ore",
+		planet_key: String = "") -> void:
+	var stable_id: String = planet_key if planet_key != "" else planet_name
 	extractors.append({
 		"position": at_position,
+		"planet_id": stable_id,
 		"planet_name": planet_name,
 		"resource_type": resource_type,
 		"inventory": INVENTORY.new(),
@@ -909,7 +914,7 @@ func add_extractor(planet_name: String, at_position: Vector2, resource_type: Str
 	# so the Planet node is already in the tree with its _ready() long since
 	# run. Without this it kept showing no derrick until it happened to
 	# despawn and respawn, which reads as the build having done nothing.
-	extractor_added.emit(planet_name)
+	extractor_added.emit(stable_id)
 
 
 func extractor_stock(index: int) -> int:
diff --git a/GasVentField.gd b/GasVentField.gd
index 831ca4c..8ad7e51 100644
--- a/GasVentField.gd
+++ b/GasVentField.gd
@@ -6,7 +6,7 @@ var progress: float = 0.0
 var emission_phase: float = 0.0
 func _ready() -> void:
 	var rng := RandomNumberGenerator.new()
-	rng.seed = hash(GameState.planet_name)
+	rng.seed = hash(GameState.planet_id if GameState.planet_id != "" else GameState.planet_name)
 	for i in range(6): vents.append(Vector2(rng.randf_range(-800,800), rng.randf_range(-650,650)))
 	queue_redraw()
 func _process(delta: float) -> void:
diff --git a/Planet.gd b/Planet.gd
index 4d17d84..954af57 100644
--- a/Planet.gd
+++ b/Planet.gd
@@ -14,6 +14,7 @@ const PLANET_DEFINITIONS = preload("res://PlanetDefinitions.gd")
 # while the fleet as a whole was clearly sitting on the planet.
 
 @export var planet_name: String = ""
+@export var planet_id: String = ""
 @export var definition_id: String = PLANET_DEFINITIONS.DEFAULT_DEFINITION_ID
 @export var landing_radius: float = 140.0
 # Set by whoever spawns this planet (PlanetField, seeded from the chunk's
@@ -67,7 +68,9 @@ func _ready() -> void:
 	visual = definition.visual_scene.instantiate()
 	visual.configure(shape_seed)
 	get_node("VisualHost").add_child(visual)
-	shows_extractor = GameState.has_extractor_at(planet_name)
+	if planet_id == "":
+		planet_id = planet_name
+	shows_extractor = GameState.has_extractor_at(planet_id)
 	GameState.extractor_added.connect(_on_extractor_added)
 	queue_redraw()
 
@@ -75,7 +78,7 @@ func _ready() -> void:
 func _on_extractor_added(built_on: String) -> void:
 	# Only the planet it was actually built on, and only a redraw when the
 	# answer really changed - every other planet in range gets this too.
-	if built_on != planet_name or shows_extractor:
+	if built_on != planet_id or shows_extractor:
 		return
 	shows_extractor = true
 	queue_redraw()
diff --git a/PlanetAtmosphereController.gd b/PlanetAtmosphereController.gd
index 3a66ea4..9363981 100644
--- a/PlanetAtmosphereController.gd
+++ b/PlanetAtmosphereController.gd
@@ -113,6 +113,7 @@ func _on_enter_pressed() -> void:
 	GameState.return_world_position = current_planet.position
 	GameState.return_camera_zoom = camera.zoom.x
 	GameState.planet_name = current_planet.planet_name
+	GameState.planet_id = current_planet.planet_id
 	GameState.planet_definition_id = current_planet.definition_id
 
 	var tween: Tween = create_tween()
diff --git a/PlanetField.gd b/PlanetField.gd
index 6a8c3c6..21ea1fc 100644
--- a/PlanetField.gd
+++ b/PlanetField.gd
@@ -83,6 +83,7 @@ func _spawn_chunk_planet(chunk: Vector2i) -> void:
 	var planet: Node2D = planet_scene.instantiate()
 	planet.position = origin + data.local_pos
 	planet.planet_name = data.name
+	planet.planet_id = data.planet_id
 	planet.shape_seed = data.shape_seed
 	planet.definition_id = String(data.get("definition_id", "rocky"))
 	# Deferred: update_chunks() can run synchronously from inside a
diff --git a/WorldGen.gd b/WorldGen.gd
index 5e73ee5..7cc6c6c 100644
--- a/WorldGen.gd
+++ b/WorldGen.gd
@@ -91,7 +91,8 @@ static func planet_data_at_chunk(chunk: Vector2i) -> Dictionary:
 	var definition: Resource = PLANET_DEFINITIONS.get_definition(definition_id)
 	var names: PackedStringArray = definition.names
 	var planet_name: String = names[rng.randi() % names.size()]
-	return {"local_pos": local_pos, "name": planet_name, "shape_seed": shape_seed,
+	var planet_id: String = "chunk:%d:%d" % [chunk.x, chunk.y]
+	return {"planet_id": planet_id, "local_pos": local_pos, "name": planet_name, "shape_seed": shape_seed,
 		"definition_id": definition_id}
 
 
diff --git a/WorldMapContent.gd b/WorldMapContent.gd
index 5d4667b..9577163 100644
--- a/WorldMapContent.gd
+++ b/WorldMapContent.gd
@@ -50,7 +50,7 @@ func building_markers() -> Array:
 func chunk_has_extractor_badge(chunk: Vector2i) -> bool:
 	if not WorldGen.has_planet_at_chunk(chunk):
 		return false
-	return GameState.has_extractor_at(WorldGen.planet_data_at_chunk(chunk).name)
+	return GameState.has_extractor_at(WorldGen.planet_data_at_chunk(chunk).planet_id)
 
 
 func _regular_polygon(center: Vector2, radius: float, sides: int, phase: float = 0.0) -> PackedVector2Array:
diff --git a/tests/test_extractor_building.gd b/tests/test_extractor_building.gd
index 0a4b769..0e52c21 100644
--- a/tests/test_extractor_building.gd
+++ b/tests/test_extractor_building.gd
@@ -135,7 +135,7 @@ func _process(delta: float) -> bool:
 				return true
 			controller._confirm_build()
 
-			var built: bool = game_state.has_extractor_at(planet2.planet_name)
+			var built: bool = game_state.has_extractor_at(planet2.planet_id)
 			var charged: bool = game_state.rocks == rocks_before - GameState.EXTRACTOR_COST
 			print("over planet '%s': enabled=%s built=%s rocks %d->%d charged=%s" % [
 				planet2.planet_name, button.enabled, built, rocks_before, game_state.rocks, charged
diff --git a/tests/test_planet_extractor_marker.gd b/tests/test_planet_extractor_marker.gd
index ed4b4cb..ef11c84 100644
--- a/tests/test_planet_extractor_marker.gd
+++ b/tests/test_planet_extractor_marker.gd
@@ -28,6 +28,7 @@ var scene: Node
 var map_content: Node2D
 var planet_chunk: Vector2i
 var planet_name: String = ""
+var planet_id: String = ""
 var stage: int = 0
 var already_spawned: Node2D
 
@@ -43,7 +44,9 @@ func _initialize() -> void:
 			var chunk: Vector2i = Vector2i(x, y)
 			if WorldGen.has_planet_at_chunk(chunk):
 				planet_chunk = chunk
-				planet_name = WorldGen.planet_data_at_chunk(chunk).name
+				var data: Dictionary = WorldGen.planet_data_at_chunk(chunk)
+				planet_name = data.name
+				planet_id = data.planet_id
 				found = true
 				break
 		if found:
@@ -61,6 +64,7 @@ func _initialize() -> void:
 func _spawn_planet() -> Node2D:
 	var planet: Node2D = load("res://Planet.tscn").instantiate()
 	planet.planet_name = planet_name
+	planet.planet_id = planet_id
 	planet.shape_seed = 12345
 	scene.add_child(planet)
 	return planet
@@ -90,7 +94,7 @@ func _process(_delta: float) -> bool:
 			# having done nothing at all. Spawning a fresh planet afterwards
 			# (as the checks below do) cannot catch that.
 			already_spawned = clean
-			game_state.add_extractor(planet_name, WorldGen.chunk_origin(planet_chunk))
+			game_state.add_extractor(planet_name, WorldGen.chunk_origin(planet_chunk), "ore", planet_id)
 			stage = 1
 			return false
 		1:
@@ -141,6 +145,7 @@ func _process(_delta: float) -> bool:
 			# by name, and getting that wrong would light up every planet.
 			var other: Node2D = load("res://Planet.tscn").instantiate()
 			other.planet_name = planet_name + " II"
+			other.planet_id = planet_id + ":other"
 			other.shape_seed = 999
 			scene.add_child(other)
 			if other.shows_extractor:
diff --git a/tests/test_planet_unique_identity.gd b/tests/test_planet_unique_identity.gd
new file mode 100644
index 0000000..d03ff09
--- /dev/null
+++ b/tests/test_planet_unique_identity.gd
@@ -0,0 +1,39 @@
+extends SceneTree
+
+
+func _initialize() -> void:
+	var state: Node = root.get_node("GameState")
+	state.extractors.clear()
+	var first_by_name: Dictionary = {}
+	var first: Dictionary = {}
+	var second: Dictionary = {}
+	for x in range(-60, 61):
+		for y in range(-60, 61):
+			var chunk := Vector2i(x, y)
+			if not WorldGen.has_planet_at_chunk(chunk):
+				continue
+			var data: Dictionary = WorldGen.planet_data_at_chunk(chunk)
+			if first_by_name.has(data.name):
+				first = first_by_name[data.name]
+				second = data
+				break
+			first_by_name[data.name] = data
+		if not second.is_empty():
+			break
+	if second.is_empty():
+		return _fail("could not find two generated planets sharing a display name")
+	if first.planet_id == second.planet_id:
+		return _fail("duplicate display names also shared a stable id")
+	state.add_extractor(first.name, Vector2.ZERO, "ore", first.planet_id)
+	if not state.has_extractor_at(first.planet_id):
+		return _fail("extractor was not attached to its planet id")
+	if state.has_extractor_at(second.planet_id):
+		return _fail("'%s' inherited an extractor from its namesake" % second.name)
+	print("same name '%s', distinct ids %s and %s" % [first.name, first.planet_id, second.planet_id])
+	print("TEST_PLANET_UNIQUE_IDENTITY: PASS")
+	quit(0)
+
+
+func _fail(message: String) -> void:
+	print("TEST_PLANET_UNIQUE_IDENTITY: FAIL (%s)" % message)
+	quit(1)