Talk to Petra

Speak to Petra Venj at the Vestian Outpost.
"A rogue Kell. Fascinating. With the exception of the House of Exile, the Fallen usually try their best to stay out of each others' way. That's why the system is parcelled up so neatly. Winter on Venus, Exiles on the Moon, Kings and Devils keeping to their own areas of the Cosmodrome. Now, there's an entire House bent on taking ground from the others." - Ghost
Added In
The Taken King (2015.09.09)