I take it New Scientist is an unimpeachable source and so I'll buy this Professor's analysis. BTW as a kid I loved space travel , wanted to be an astronaut , built a scale model of Saturn V , watched all the space landings in a state of childish euphoria and dreamed those dreams. I'm hopefully more adult and rational in my choices now. Let's solve the problems on earth now rather than blasting into space at enormous cost. Why space is the impossible frontier Hawking, Obama and other proponents of long-term space travel are making a grave error. Humans cannot leave Earth for the several years that it takes to travel to Mars and back, for the simple reason that our biology is intimately connected to Earth. To function properly, we need gravity. Without it, the environment is less demanding on the human body in several ways, and this shows upon the return to Earth. Remember the sight of weakened astronauts emerging after the Apollo missions? That is as nothing compared with what would happen to astronauts returning from Mars.