Gravitar is out to conquer the universe! Gravity is his lethal weapon. First, he bombards each galaxy with hostile gravitational forces. Then, in each galaxy's solar system, he installs a powerful reactor, creating a killer sun which destroys all life on the surrounding planets. He blockades those planets with deadly rammers and automated bunkers programmed to shoot any and all would-be defenders. So far, his deadly plan has conquered four galaxies, each of which contain three solar systems.
Your galaxy is under threat of attack from Gravitar. The only possible way to stop him is to break his hold on the four galaxies. You can either destroy the bunkers on all the planets, or activate the reactor at the core of the Alien Reactor Base and escape before the deadly explosion. Each planet has a treacherous landscape and an even more dangerous gravitational field. Time is running out--Gravitar is coming closer!