This Assignment first takes place during your first visit to the Citadel once you have exposed Saren and become a Spectre. There are alternative methods to being this Assignment.
How to Begin:
There are several ways to begin this Assignment, with the earliest being from Admiral Kahoku on the Citadel:
After exposing Saren and becoming a Spectre, return to the Citadel Tower and look to the left of the stairs leading to the Council Chambers, you’ll find Admiral Kahoku. Agreeing to assist him with his request will begin this Assignment. Alternatively, Captain Anderson will direct you to Kahoku if you ask him about Banes following the completion of the Doctor Michel Assignment.
You can also pick this Assignment up by heading directly to the Sparta System in Artemis Tau. From here, approach Edolus to recieve a distress call.
With the Assignment accepted, make your way to the Sparta System in the Artemis Tau Cluster where you’ll find the planet Edolus. Once you’re planetside, open your map and look for the Distress Signal to your north, taking care to save your game before you approach it. As you do, you’ll be attacked by a Thresher Maw and if this is your first time encountering these deadly foes, you’ll want to be extra careful.
You’ll want to avoid the Thresher Maw getting close to the Mako as a direct hit will be almost fatal to you. Keeping your distance however, will see the Thresher Maw spit a barrage of acid your way, this can be avoided by simply jumping while stationary. The final attack to watch out for is when the Thresher Maw begins burrowing towards you while it’s Sensory Tentacles will appear above ground. The intended method here is to drive around at speed, defeating the tentacles while avoiding the oncoming Thresher Maw however there is a trick you can use. If you drive far enough away from the Thresher Maw, it’ll retreat back underground and wait for you to approach it again, without the Sensory Tentacles. It’s health will remain the same so you can abuse this so that you never have to deal with that attack.
Regardless of how you deal with the Thresher Maw, once it’s defeated, make your way to the pile of bodies and examine one of them to learn that it looks like they were lured by the Distress Signal by another party. With all said and done, there’s nothing left to do but make your return to the Citadel and deliver the news to him to complete the Assignment. Completion of this Assignment will unlock the follow-up, UNC: Cerberus when you access the Galaxy Map.