These are the missing practical arguments: safeguarding the Earth from otherwise inevitable catastrophic impacts and hedging our bets on the many other threats, known and unknown, to the environment that sustains us. Without these arguments, a compelling case for sending humans to Mars and elsewhere might be lacking, But with them—and the buttressing arguments involving science, education, perspective, and hope—I think a strong case can be made. If our long-term survival is at stake, we have a basic responsibility to our species to venture to other worlds.
Sailors on a becalmed sea, we sense the stirring of a breeze.
- - Pale Blue Dot: A Vision of the Human Future in Space by Carl Sagan, 1994.