Justice Prime

Justice Prime was a small and cold planet, so cold that the nitrogen on the surface was turned into snow as it moved away from the sun. It was the only planet in the Justicia system not to have a circular orbit, and the only planet whose surface was entirely inhospitable to human life. It also had lower gravity than Earth. As such, all buildings on Justice Prime were carved out underground, where gravity and atmosphere could be regulated.

This planet was the first to be used as a prison planet, specifically for alien criminals. The criminals were kept underground in the SCAT-house, where they were forced to lead experiments and develop technologies that the Justicia company would sell at a profit. The Ninth Doctor was sent to Justice Prime after being arrested for trespass on Justice Alpha. (PROSE: The Monsters Inside)