It's the foundation of Superman's origin: He was sent, as a baby, from the planet of Krypton, which exploded just seconds after his ship got clear of the atmosphere. Superman is the ultimate immigrant, a man who has never really known his home. And now, he might have to destroy it all over again, in Action Comics Annual #2.
That's the thrust of Krypton Returns, a new crossover spanning the Superbooks and exploring the relation Superman, Supergirl, and Superboy have with Krypton. H'El, who you might remember was going to destroy the Earth to rebuild his home, recently got a nasty shock in Villain's Month when he discovered he wasn't who he thought he was, and that his origin is far different from what he was led to believe.
So Krypton has been rebuilt, partially to get H'El some answers. Of course, the bigger problem is that the Super "Family" doesn't really get along, as you'll see in these opening pages. The full story arrives next week.