Human journeys into space fill us with wonder. But the thrill of space travel for astronauts comes at enormous expense and is fraught with peril. As our robot explorers grow more competent, governments and corporations must ask, does our desire to send astronauts to the Moon and Mars justify the cost and danger? Martin Rees believes that beyond low-Earth orbit, space exploration should proceed without humans.

The United Kingdom’s Astronomer Royal, Martin Rees was previously Professor of Astronomy and Director of the Institute of Astronomy at the University of Cambridge. His latest book, co-written with Donald Goldsmith, is The End of Astronauts. ​Mark Lee is an Emeritus Professor of Computer Science who has researched AI and robotics for 40 years and is author of How to Grow a Robot: Developing Human-Friendly, Social AI.