... the dead titan you find in the first moon mission was part of Eris' fireteam? In the first moon mission, your ghost says the guardian you are tracking made his basecamp in the mushroom shaped tower in Anchor of Light. Later, Eris says that's where her fireteam held up before entering the Temple of Crota. Also, one of the titan marks she sells basically says it used to belong to a member of her fireteam (don't remember which one). The dead titan on the moon is not wearing a class item. She also mentions that a member (or members) of her fireteam died before entering the Temple of Crota, which is where you find the body.