Forty years ago today, humans accomplished a goal as old as the species when two men walked on the Moon. We talk with Moonwalker Number Two about the Moon itself and the depression and alcoholism he faced on returning to Earth. Buzz Aldrin is among those who say the Moon itself is a dead end, but that humans could get to Mars before 2050. He insists that we should. Others point out that we've been there for five years, with robots, which make more precise observations and never need to come home.