Eventually, their sun converted from a yellow dwarf to a red giant, so the Puppeteers moved the "Fleet of Worlds", the five planets, to their system's Oort cloud. This is one of the reasons the Puppeteers were so successful at keeping the location of their homeworld a secret—explorers would be looking for a yellow dwarf (as one could surmise that Puppeteers had evolved around a yellow dwarf from their biology and that they were comfortable on Earth-like planets without pressure suits) when their planet(s) were actually near a red giant.