Molech

Molech is a Knight world in Segmentum Solar where the Emperor once walked into a warp gate and came back with the knowledge to make Primarchs. House Devine ruled from Lupercalia until they turned their coats and opened the door for Horus and Mortarion. Most of the garrison died; the Scouring took the planet back. Jambonium's plot is a low-confidence Solar guess, not a surveyed lock.