I'm looking for a (possibly animated) Science Fiction movie in which aliens, I think, installed a device that would cool down the Earth's core. To save their planet, one billion humans got on a gigantic spaceship and travelled to the planet of the aliens to get something to turn that device off. The spaceship was so big it had an ocean with dolphins inside. The people on it lived in "cities" labelled 1.1, 1.2, 1.3, etc. and were somehow ordered alphabetically by last name.
That's about all my ten year old son can remember. He says there was also a book series with about four volumes that tells the same story.
The movie was at least one or two years old, possibly more, and dubbed in German. It may have been rated (in Germany) for 12 year olds (despite my son's age at that time).