Just a few notes that may tie in to the game...
0720 Hours: The Covenant destroys ODG Facility A-331 by aerial bombardment (glassing), though some Spartans escape. The surviving MAC guns are now offline and are quickly destroyed by plasma torpedoes. Remaining UNSC vessels have no choice but to retreat. The Covenant warships are split into two groups: 5 ship teams that hunt down the surviving UNSC vessels and a group of ships that align themselves in formation and begin to glass Reach.
"We are not wasting a single UNSC ship to confirm what we have already seen a dozen times before: Reach is gone. Everything on it is blasted to bits, burned, glassed over, and vaporized. Everyone on Reach is dead. Dead. Dead. Dead."
Colonel James Ackerson[13]
The Forerunner Crystal, referred to by the Covenant as the Fragment of Divinity, the Shard of the Gods,[1] or the Holy Light,[2] was a Forerunner artifact that was discovered in the underground Menachite Forerunner Complex on Reach by Dr. Catherine Elizabeth Halsey and the surviving Spartan members of Red Team in 2552.[3] The artifact is of incredible potential, capable of warping space,[4] energy,[4] gravity,[5] and even time and Slipspace.[6] It is hardly understood by the UNSC forces who found it, but is a prize that the Covenant were extremely eager to obtain.
September 2552
September 7th
* 0002 Hours: The SPARTAN Red team survivors and Dr. Halsey, after days of walking through the abandoned Titanium mines below CASTLE base, reach a corridor covered in Forerunner symbols.
o shortly afterwards: A series of detonations by Covenant forces looking for them cause the deaths of Vinh-030 and Isaac-039.
The unofficially dubbed "Legendary Planet" is a mysterious planet toward which the rear section of the UNSC Frigate Forward Unto Dawn, containing the Master Chief and Cortana, is seen drifting into the Legendary ending of Halo 3. Seconds later, a light shines across the surface of the planet, as the Forward Unto Dawn is caught by the planet's gravity. The Legendary Planet also appears in a small image in the Halo Encyclopedia, where it is shown to have a reddish-orange color on a small illuminated section.[1]
Reach
The last theory is that the planet is, in fact, the planet Reach. This can be concluded from the nebula cloud being similar to that that was in the Starry Night trailer, during the conversation between the boy and the girl. Other evidence that supports this is that the lake seen on Reach is similar to the symbol that can be seen on the planet, which would be a dry lake bed from the planet being glassed. Since Reach was glassed, not destroyed, it is safe to assume that the planet could be Reach. The very last bit of information that points towards the legendary planet being Reach is in fact the last level, is one of the section names. Full circle, indicates that every thing is coming to an end, where it all began. The first game began with Master Chief in a cryo chamber, and it is known that they had left from Reach, and Halo 3 ended with Master Chief climbing into a cryo chamber, with the back half of the ship heading towards a planet that bears resemblence to Reach.