An international team led by researchers at Queen's University Belfast has made a discovery that has eluded astronomers for decades. Beginning in 1906, telescope observations revealed a population of asteroids leading and trailing Jupiter, which came to be known as the "Trojan" and "Greek" populations. Since then, astronomers have discovered similar "families" orbiting Saturn and Uranus, but not Neptune. Thanks to the Queen's-led team, the mystery of the missing Trojans has now been resolved.