Lucy is a planned NASA space probe that will tour five Jupiter trojans, asteroids which share Jupiter’s orbit around the Sun, orbiting either ahead of or behind the planet and one main belt asteroid. All target encounters will be fly-by encounters.
On 4 January 2017, Lucy was chosen, along with the Psyche mission, as NASA’s Discovery Program missions 13 and 14 respectively. The mission is named after the ‘Lucy’ hominid skeleton, because the study of Trojans could reveal the “fossils of planet formation”: materials that clumped together in the early history of the Solar System to form planets and other bodies.
Lucy is planned to launch in 2021. In 2025 it will fly by the inner main-belt asteroid 52246 Donaldjohanson, which was named for the discoverer of the Lucy hominid fossil. In 2027 it will arrive at the L4 Trojan cloud (a group of asteroids that orbits about 60° ahead of Jupiter), where it will fly by four Trojans, 3548 Eurybates, 15094 Polymele, 11351 Leucus, and 21900 Orus. After these flybys, Lucy will return to the vicinity of the Earth whereupon it will receive a gravity assist to take it to the L5 Trojan cloud ...