At the end of the Halo 3 credits, the ship Master Chief escaped on seems to land across a planet. Is anything known about this planet, and whether or not this landing leads into Halo 4?
If you take a look at the upcoming Halo 4 trailer, you can see a superstructure that seems to be pulling in the ship.
The planet itself is Sigma 7, or more properly, "Requiem", which seems to be close to Installation 00, and according to the Halo Wiki:
The planet is littered with blue-glowing symbols and geometric patterns - clearly Forerunner in origin.
Speculation: The Marathon symbol can be seem, which is meant to indicate a Reclaimer (person that has to activate the Halo super-weapon), so it could be a place for reclaimers to seek shelter or activate the weapon.
In the Halo Anniversary terminal videos, Guilty Spark talks about deploying the Halo array, and mentions that everything the Forerunners knew could be destroyed. When he says that, the image of the planet is flashed, so the planet could be similar to the Library or some other form of vast knowledge database.