The rest of Pale Blue Dot turns to the future. Chapter 19 concerns terraforming and the possibility of humans living on other worlds. The chapter opens with the first mention of “terraforming” in print: the 1942 science-fiction short story “Collision Orbit,” by Jack Williamson for Astounding Science Fiction. The story is about humans living on an asteroid, and Sagan weighs Williamson’s imagination against what might be possible. While Sagan doubts artificial gravity will be possible, the idea of living on other planets inside domes or underground caverns full of oxygen are scientific possibilities. Williamson imagines a power source of antimatter; while Sagan acknowledges that little is known about generating antimatter, he does not reject the possibility of running a colony or engine using the gamma rays emitted by matter and antimatter interactions. He also considers other possible power sources such as solar, deuterium, tritium, and fusion reactors.

Sagan considers the possibilities of engineering a planet’s surface and atmosphere for human life. He claims that he was the first person to discuss terraforming as a possibility in a scientific publication, writing on Venus in 1961. That article, written before humans knew about the acidic clouds and extreme surface temperature, suggested methods for reversing Venus’s greenhouse effect by removing carbon dioxide from the atmosphere.