Last March, many cosmologists were disappointed when new measurements of the cosmic microwave background showed no signs of exotic physics such as previously undiscovered particles. Or did they? In separate papers, three groups of theorists now argue that last year's data, combined with measurements of how galaxy clusters are scattered through space, suggest that some of the universe's dark matter consists of a new particle called a sterile neutrino. Further studies now in progress may soon show whether the hypothesized hot, fast-moving particles are real. Meanwhile, physicists are savoring the possibility that the universe is more exciting than they had assumed.