Chapter 19, Remaking the Planets, Chapter 20, Darkness Summary and Analysis

Sagan speculates that men might be able to live inside of asteroids, particularly carbon ones; the materials in asteroids could be used to synthesize products. Organic solids could be burned as fuel as well. Anti-matter might do as well, and mass manufacture of anti-matter may be available by the 22nd century.

"Terraforming" or modifying a planet for life would be feasible on Mars, where there is plenty of sunlight, water and carbon dioxide. As time progressed permanent colonies could be staffed. A new age of colonization may arise. And perhaps the Martian environment could be engineered so that men could live without elaborate settlement superstructures.

Sagan then examines the terraforming idea in more detail. Terraforming Venus would require reducing its greenhouse effect and blowing away much of its atmosphere. Mars would...