Hey Guys, I was going through the halo games and as we all know the planet structure in the teaser was forerunner. In Halo 1 the monitor said that the Halo rings have a massive radius to destroy all sentient life.
HALO 4:Maybe this Forerunner structure is made to be a Beacon/Radio type thing they made to relay communications between Halo Rings and other Forerunner Structures. So maybe Master Chief uses it to communicate with Earth. I would think they would do this at something like the control room which I think would be in the middle of the Electric type things in the middle of the planet in the teaser. Maybe during the way to the control room type place, Master Chief plugs in Cortana into a Forerunner A.I. Port to activate another Dreadnought Forerunner ship to get off the Planet, but while she is in the Forerunner A.I system, the Millenniums and Millenniums of Forerunner history infects her. Master Chief then has to put Cortana is his head because from personal experiences from the Spartan-2 program, he remembered that Halsey had connected Cortana and her older sister Kalmiya(Which Halsey secretly kept). After fighting the infection from Cortana he finds that Halsey is in Cryo-Sleep along with the remaining Spartans-2s and 3s are on Onyx.
HALO 5: He gets to Onyx with the Dreadnought. He wakes up Halsey to fix Cortana. She will then use parts from Kalmiya to fix Cortana. Using the Dreadnought to get back to the teaser planet to receive coordinates to Earth using the control room.They then blow up the planet by destroying reactors that create the electricity in the middle of the planet. At the last second they use the Dreadnought to get away from the planet while it's collapsing.
HALO 6:Unknowingly Forerunner are on the ship that were still on it since the original planet in the teaser. When they get to Earth the Forerunners hide for months and send out beacons from the Dreadnought . In Halo 6 the Forerunners attack Earth for destroying the Halo Rings and the Ark. In the end Master Chief and the Arbiter team up for a few levels before the Arbiter dies. In the last levels they send Master Chief as a bait to get all the Forerunners in the same place to destroy them all at once. Master Chief then sacrifices himself for the Human Race. They them live without the threat from the Covenant, Flood and the Forerunners.
Hope you enjoyed reading my thoughts of what I think this trilogy will be. Leave comments of what you think. Thanks for reading.