Hopefully in the story, or sidequest, or a dlc I don't care which we get to find out who built the exo. Maybe a counter force anpgainst the Vex? A weaponized ghost companion? Souls of those returned from the void?
Edited: 7/29/2014 5:02:12 AM PermalinkActually Pluto got mad we stopped calling it a planet, developes the "exo's"(which is an ancient sumerian word for darkness if i recall my days at the academy) to destroy us all and the traveller came and saved the day as a giant magnet, erasing the exo's nefarious plan. check and mate.