A team of astronomers led by the University of Hawaii's Institute for Astronomy have found evidence that asteroids change colour as they get older. The team used data from the Sloan Digital Sky Survey (SDSS), which has accurate colour measurements on 100,000 asteroids. They found that asteroids turn redder over time because of the constant bombardment of radiation from the Sun and cosmic rays. With more research, astronomers should soon be able to judge the age of an asteroid just by its colour.