Could be Onyx or maybe Reach.
As the Reaver dude says, thats unlikely because the Onyx shield world contains certain surviving main characters that I find unlikely to appear in the first of this new trilogy, or at all perhaps. (no names, avoiding spoilers).
In the book 'Ghosts of Onyx' the planets outer surface is stripped away by an amazing combination of Sentinels (like Devastator in Transformers!) to reveal an inner metal planet, referred to as a 'Shield world' by the Forerunners.
This looks likely to be happening to Reach at the end of the game, so in theory there could be at least two Shield worlds out there, probably more.
It seems the Shield worlds were built to protect the Forerunners when they activated the Halo array, but a complicated story involving Mendicant Bias meant the 'gun at the head of the universe' was fired before they had a chance to board them. Maybe...
The shield worlds are like a huge inside-out planet, with a sun in the middle and the surface being on the inside. At least thats how its described in the book.
I'm too old to be this excited by yet another Halo game, and I type too much!
