The Second Exodus: the sky was blue image - The Enceladus Initiative mod for Portal 2

Year 2552... The Earth is no longer habitable since year 2401 due to the atmosphere collapse and temperature rise. Human race has been forced to live in the different colonized planets into the Solar System. This was called "The Second Exodus". After the "Enceladus Atmosphere Implementation Program" (EAIP) succeeded in year 2295, Saturn's moon Enceladus turned into the most important human colony into the Solar System altogether with Titan's. After the EAIP implementation, Aperture Laboratories developed their more ambitious testing program, The Enceladus Initiative.