Buzz Aldrin in 1969 became the second human to walk on the Moon, and now he believes humans could walk on Mars as soon as 2040. Achieving that goal would be a huge challenge. The journey would be complex and very expensive. Aldrin suggested the United States would need to partner with other countries in the effort. Plus, the first explorers to go to Mars would likely have to stay there forever to start a new civilization. Still, the legendary astronaut believes it would be a worthwhile undertaking. If a plan was announced soon — such as in 2019, on the 50th anniversary of the Apollo 11 Moon landing — a generation of astronauts would grow up dreaming of being the first settlers on Mars, Aldrin said.