Arbiter has been extracted, now the Fireteam will team up with him to search Guardian in Sunaion and the final Coven base on Sanghelios. Locke must examine and research for this Guardian in Sunaion with the help of Dr. Halsey in Mission 9: Alliance.
You'll Continue with the Fireteam in Mission 9, where you need to locate and examine the area, report to Dr. Halsey in order to find the exact location on the Map. This is a very short mission so just relax and complete it with ease.
First Locate and head to Dr. Halsey to report her on the current progress as she is unable to share details with you after looking at Cortana's power. Later you need to find Palmer to get the coordinates of the nearby support station. If you think your lost feel free to use the D-pad and get on Track.
Hint: Before you head towards Dr. Halsey simply check the D-pad with new information and nearby collectibles.
Once you locate Palmer, she will take you into the Pelican, but before you head towards the Pelican just take a look at the left section and pick up the intel piece. Thus ending the Mission 9: Alliance and the cutscene will begin.