22 December 2008 - Enceladus

Pollution must be OK, if even advanced space aliens don’t worry about it. The alien base hidden inside Enceladus is powered by a giant five gigawatt fusion reactor (unless they have something even more advanced), but they’re being so sloppy with their waste heat that they polluted the whole Saturn system and gave themselves away. Either that, or humans are so harmless that they don’t care.