Whatever it is it will bring Destiny 1 to a close so it should be pretty epic or apocalyptic. I'm guessing it's to do with the Traveller or the Origins of the Traveller. If it's Mars related remember waaay back pre release when Thorn was going to be a reward from Charlemagnes vault? Might be the Cabal are looking for that. They were trying to Hack the warmind in Buried City mission but Rasputin had locked it down. There's a lot of stuff to cover still I guess. :)