===================================================================
--- original.js
+++ change.js
@@ -1,142 +1,146 @@
-/****
+/**** 
 * Classes
 ****/
 // Missile class
 var Missile = Container.expand(function () {
-  var self = Container.call(this);
-  var missileGraphics = self.attachAsset('missile', {
-    anchorX: 0.5,
-    anchorY: 0.5
-  });
-  self.speed = 10;
-  self.move = function () {
-    self.y -= self.speed;
-  };
+	var self = Container.call(this);
+	var missileGraphics = self.attachAsset('missile', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.speed = 10;
+	self.move = function () {
+		self.y -= self.speed;
+	};
 });
 // Alien class
 var Alien = Container.expand(function () {
-  var self = Container.call(this);
-  var alienGraphics = self.attachAsset('alien', {
-    anchorX: 0.5,
-    anchorY: 0.5
-  });
-  self.speed = 2;
-  self.move = function () {
-    self.y += self.speed;
-  };
+	var self = Container.call(this);
+	var alienGraphics = self.attachAsset('alien', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.speed = 2;
+	self.move = function () {
+		var dy = earth.y - self.y;
+		var dx = earth.x - self.x;
+		var angle = Math.atan2(dy, dx);
+		self.x += self.speed * Math.cos(angle);
+		self.y += self.speed * Math.sin(angle);
+	};
 });
 
-/****
+/**** 
 * Initialize Game
 ****/
 var game = new LK.Game({
-  backgroundColor: 0x000000 // Init game with black background
+	backgroundColor: 0x000000 // Init game with black background
 });
 
-/****
+/**** 
 * Game Code
 ****/
-// Game variables
 // Initialize assets used in the game.
+// Game variables
 var missiles = [];
 var aliens = [];
 var earth;
 var scoreTxt;
 var spawnAlienInterval = 120; // Frames until a new alien spawns
 var nextAlienSpawn = spawnAlienInterval;
 // Initialize Earth
 function initEarth() {
-  earth = game.addChild(LK.getAsset('earth', {
-    anchorX: 0.5,
-    anchorY: 0.5,
-    x: game.width / 2,
-    y: game.height - 200
-  }));
+	earth = game.addChild(LK.getAsset('earth', {
+		anchorX: 0.5,
+		anchorY: 0.5,
+		x: game.width / 2,
+		y: game.height - 200
+	}));
 }
 // Initialize score display
 function initScore() {
-  scoreTxt = new Text2('0', {
-    size: 150,
-    fill: "#ffffff"
-  });
-  scoreTxt.anchor.set(0.5, 0);
-  LK.gui.top.addChild(scoreTxt);
+	scoreTxt = new Text2('0', {
+		size: 150,
+		fill: "#ffffff"
+	});
+	scoreTxt.anchor.set(0.5, 0);
+	LK.gui.top.addChild(scoreTxt);
 }
 // Fire a missile
 function fireMissile(x, y) {
-  var missile = new Missile();
-  missile.x = x;
-  missile.y = y;
-  missiles.push(missile);
-  game.addChild(missile);
+	var missile = new Missile();
+	missile.x = x;
+	missile.y = y;
+	missiles.push(missile);
+	game.addChild(missile);
 }
 // Spawn an alien
 function spawnAlien() {
-  var alien = new Alien();
-  alien.x = Math.random() * (game.width - alien.width) + alien.width / 2;
-  alien.y = -alien.height / 2;
-  aliens.push(alien);
-  game.addChild(alien);
+	var alien = new Alien();
+	alien.x = Math.random() * (game.width - alien.width) + alien.width / 2;
+	alien.y = -alien.height / 2;
+	aliens.push(alien);
+	game.addChild(alien);
 }
 // Check for collisions
 function checkCollisions() {
-  for (var m = missiles.length - 1; m >= 0; m--) {
-    for (var a = aliens.length - 1; a >= 0; a--) {
-      if (missiles[m].intersects(aliens[a])) {
-        aliens[a].destroy();
-        aliens.splice(a, 1);
-        missiles[m].destroy();
-        missiles.splice(m, 1);
-        LK.setScore(LK.getScore() + 1);
-        scoreTxt.setText(LK.getScore());
-        break;
-      }
-    }
-  }
+	for (var m = missiles.length - 1; m >= 0; m--) {
+		for (var a = aliens.length - 1; a >= 0; a--) {
+			if (missiles[m].intersects(aliens[a])) {
+				aliens[a].destroy();
+				aliens.splice(a, 1);
+				missiles[m].destroy();
+				missiles.splice(m, 1);
+				LK.setScore(LK.getScore() + 1);
+				scoreTxt.setText(LK.getScore());
+				break;
+			}
+		}
+	}
 }
 // Game over check
 function checkGameOver() {
-  for (var i = 0; i < aliens.length; i++) {
-    if (aliens[i].intersects(earth)) {
-      LK.effects.flashScreen(0xff0000, 1000);
-      LK.showGameOver();
-      break;
-    }
-  }
+	for (var i = 0; i < aliens.length; i++) {
+		if (aliens[i].intersects(earth)) {
+			LK.effects.flashScreen(0xff0000, 1000);
+			LK.showGameOver();
+			break;
+		}
+	}
 }
 // Touch event to fire missiles
 game.on('down', function (obj) {
-  var pos = obj.event.getLocalPosition(game);
-  fireMissile(pos.x, earth.y);
+	var pos = obj.event.getLocalPosition(game);
+	fireMissile(pos.x, earth.y);
 });
 // Game tick event
 LK.on('tick', function () {
-  // Move missiles
-  for (var i = missiles.length - 1; i >= 0; i--) {
-    missiles[i].move();
-    if (missiles[i].y < -missiles[i].height) {
-      missiles[i].destroy();
-      missiles.splice(i, 1);
-    }
-  }
-  // Move aliens
-  for (var j = aliens.length - 1; j >= 0; j--) {
-    aliens[j].move();
-    if (aliens[j].y > game.height + aliens[j].height) {
-      aliens[j].destroy();
-      aliens.splice(j, 1);
-    }
-  }
-  // Spawn aliens
-  nextAlienSpawn--;
-  if (nextAlienSpawn <= 0) {
-    spawnAlien();
-    nextAlienSpawn = spawnAlienInterval;
-  }
-  // Check for collisions and game over
-  checkCollisions();
-  checkGameOver();
+	// Move missiles
+	for (var i = missiles.length - 1; i >= 0; i--) {
+		missiles[i].move();
+		if (missiles[i].y < -missiles[i].height) {
+			missiles[i].destroy();
+			missiles.splice(i, 1);
+		}
+	}
+	// Move aliens
+	for (var j = aliens.length - 1; j >= 0; j--) {
+		aliens[j].move();
+		if (aliens[j].y > game.height + aliens[j].height) {
+			aliens[j].destroy();
+			aliens.splice(j, 1);
+		}
+	}
+	// Spawn aliens
+	nextAlienSpawn--;
+	if (nextAlienSpawn <= 0) {
+		spawnAlien();
+		nextAlienSpawn = spawnAlienInterval;
+	}
+	// Check for collisions and game over
+	checkCollisions();
+	checkGameOver();
 });
 // Initialize game elements
 initEarth();
 initScore();
\ No newline at end of file