Do you know of a movie about Earth being fractured, fissured and finally broken into pieces (by a strange alien attack). The pieces get into a stable motion around the debris (like the floating mountains of Pandora but bigger). People who are in shelters in some of the pieces generate resources and supplies and build things to get the pieces into one. At the end, they manage to get all the parts back into a near-spherical shape (with the help of gravity). Then they see that this is a new moon of the old.
Are you talking about Titan AE?
Professor Tucker explains that the Titan was designed to create an Earth-like planet; however, its power cells lack the energy necessary for the process .... The re-energized Titan vaporizes the Drej mothership and molds the asteroid belt into a new habitable planet.
This sounds a bit like the story to Septerra Core, though this is a computer game. It takes place in a shattered world (Septerra), consisting of seven shells orbiting the core. In the end, the protagonists manage to unify Septerra, and they find three new worlds in their sky.
There is also Skyland, but I don't think they put that together.
There's a very high chance you're thinking of Skyland.