Richard A. Muller has never been comfortable with conventional scientific wisdom. In the 1980s, when his mentor Luis Alvarez came up with the then outrageous idea that a giant comet or asteroid impact wiped out the dinosaurs, the University of California, Berkeley, physicist went him one better, suggesting that the meteorite had been hurled our way by a dim companion star to the sun, which Muller dubbed Nemesis. In the 1990s he posited that ice ages are triggered by space debris encountered because of cyclical changes in the location of Earth’s orbit.