By exploring other worlds we safeguard this one. By itself, I think this fact more than justifies the money our species has spent in sending ships to other worlds. It is our fate to live during one of the most perilous and, at the same time, one of the most hopeful chapters in human history.
"Cosmos: A Personal Voyage". Documentary (1990 Update). Episode 13: "Who Speaks for Earth?", 1990.