We'll have to stay a while. Astronauts will need to remain on Mars or orbiting it for months at a time. A single Mars mission, from start to finish, would likely take more than two years. That's a long while to be away from our home planet, breathing recycled air in the cramped quarters of a laboratory environment. And with a 40-minute lag between sending messages to Earth and receiving responses back, astronauts will need to make autonomous decisions. All of this will contribute to extreme feelings of alienation. How does going back to the moon help?