In the previous novel, 2010: Odyssey Two, Jupiter was converted into a mini-sun which was dubbed "Lucifer" following the Soviet ship Leonov’s mission to Jupiter to find out what happened to the Discovery. A message was sent to Earth by Dave Bowman, through HAL: "ALL THESE WORLDS ARE YOURS, EXCEPT EUROPA. ATTEMPT NO LANDINGS THERE." This is due to the discovery of alien life in Europa's ocean, which was frozen over at the surface until Lucifer melted the ice and caused an atmosphere to form.