Actually it was never stated what that last barrier was. It was only stated that Kal crossing that barrier would cause the destruction of everything. Or something to that effect. It was safe for Kara to cross that barrier (according to the Spectre, anyway) because she was unconscious. Even if that "string" of planets Superboy moved was made up of moon or mars size worlds, that would still add up to moving something bigger than earth. :wink:
Are you sure? If one could move the earth, one could move literally 81 Moons---and of course, we have no idea if the planets themselves might have had some partial propulsion system to aid Superman/Superboy.
We have SEEN Superman stop the Earth in its tracks, in its orbit, without any additional power---so we're pretty sure on that one. (It seemed to take all his strength, though.) The rest there could be a LOT of variables.---Al