All-Star Comics #55 (1950)

At the latest meeting of the Justice Society they gather to watch bizarre newsreels, including one of a flying saucer and strange creatures from another planet getting out. The location of that last one makes some of the JSAers think of a scientist friend of theirs who lived in the reported area, but has been incommunicado for a while now. They visit his abandoned house and start a dictaphone playing where a message from Dr. Napier tells the heroes about mentally receiving strange formulae he can't explain, but which led him to develop a rocketship. With some clues around his house, the JSA divine that Dr. Napier was carried off by creatures from Jupiter for reasons unknown, build the ship he was designing, and use it to fly to Jupiter to rescue him. On Jupiter, the team finds a giant human being chased by aliens like the ones they saw in the newsreel. After rescuing him, the JSA's informed the "green heads" came to Jupiter and their leader is now trying to get them to conquer every planet in the solar system. Flash races in and covertly learns the helmeted leader's plans: since Earth has so many armies, he's decided not to bother conquering it and just cut the planet in half with a superweapon being built on Mars. The JSA, and the giant man they saved, pursue the leader to the red jungles of Mars. They're immediately attacked by primitive ape-men, but Wonder Woman scares them off by building a fire. Green Lantern finds the leader, who shows the hero that the rest of the JSA have put on helmets like his and become his slaves. The emerald crusader makes to attack the leader, who creates a duplicate of Green Lantern with one of his machines. Every attack Green Lantern makes is met with an equal one and the fight seems a stalemate, but Green Lantern tricks his double into firing a green fist at a wooden cabinet, which makes it bounce back and pulverize the double. He knew everything Green Lantern was going to do, but not the longstanding memory of the hero's only weakness: wood. The leader sics the rest of the Justice Society on Green Lantern, who conjures green hands with his ring and uses them to take off his teammates' helmets. The green heads fire their superweapon, but the giant humanoid the JSA rescued on Jupiter reveals he reprogrammed it to fire at the green heads' home planet, and it was destroyed instead. The JSA then unmask the leader, and reveal Dr. Napier, who was under the green heads' mind control while he wore the helmet. The ruler of the green heads is captured, ensuring the Jovian giant people can easily free themselves. The Justice Society and Dr. Napier head for home.