Nasa is gearing up to launch the Lucy mission on Saturday for a voyage that could revolutionise our knowledge of planetary origins and the formation of the solar system. A space probe will fly atop a United Launch Alliance Atlas V 401 rocket from Cape Canaveral, Florida. The mission is heading for a population of distant asteroids known as the Trojans. These primitive bodies share an orbit with Jupiter and date from the formation of our solar system. They are thought to have come from all over the solar system and so preserve a record of the conditions 4.6bn years ago when Earth and the other planets were forming. Jupiter’s mighty gravity has trapped them like flypaper over the aeons in two swarms: one preceding the planet, the other following. The journey to the Trojans will take six years. Once in space, Lucy will return to Earth for two gravitational assist manoeuvres. These will add energy to its orbit, lofting it into the preceding swarm, where it will encounter four Trojans during the 2027-28 timeframe. It will also pass a main belt asteroid en route in 2025. Lucy will return to Earth before heading into the following swarm to fly past one more Trojan in 2033. The spacecraft will continue cycling between the two Trojan swarms every six years.