Lethe (The Juggernauts)

Lethe was the planet on which Davros, masquerading as 'Professor Vaso', developed Mechanoids into 'Juggernauts' using organic material cannibalized from human victims. He was unwittingly assisted in the project by Melanie Bush. It initially had an atmosphere which was poisonous to the Daleks (but not the ones from Necros). It was originally a mining colony. (BFA: The Juggernauts)