This currently exists as a pre-installed generator only within the MultiWorld plugin. http://dev.bukkit.org/server-mods/multiworld-v-2-0/pages/worldgenerators/solarsystem/ Its perfect. I think its very ideal for a creative mode map. However the only reason I do not use MultiWorld is because I prefer the all the add-on features that is currently provided for Multiverse, especially the Multiverse Portals. I was hoping someone can make this as a world generator plugin that can be used by Multiverse. Keeping more or less the same size(s) of the spheres/planets. People can basically build on them and continue building deeper inside or connect their sphere to a friend's or a totally new one.