Voyage to the Metal Moon - Michael (Author) Dahl - Bog

Zak Nine and Erro have come up with a brilliant plan to escape. They'll simply hide on board a prison ship and ride it to freedom on another planet! Unfortunately, the boys don't get far when the ship docks at one of Planet Alcatraz's metallic moons. The hollow sphere is magnetic, and the only way to walk on it is by wearing special magnetic boots.