¶Lucy. You may picture asteroids as mostly living in the belt between Mars and Jupiter. However, two other clusters of asteroids lead and trail Jupiter in its orbit, grouped around the giant planet’s L4 and L5 points—these are known as the Jupiter Trojans, and they contain as many 1 km+ asteroids as the main belt. Whether these objects were captured during the formation of the solar system, or during Jupiter’s disruption of the giant planets’ orbits some 600 million years later as postulated by the Nice model, they are very old and represent preserved material similar in composition to the outer planets. NASA’s upcoming Lucy mission plans to visit up to 7 of these trojan asteroids, along with one asteroid in the main belt, during its 12-year mission to study the evolution of the giant planets. Fittingly, Lucy is named for the 3.2 million year old fossilized proto-human skeleton which taught us much about our own evolution. Lucy, the spacecraft, carries a high-resolution camera, spectrometers, and will measure the masses of objects its passes via precise measurements of the Doppler shift of its radio signals at Earth to figure out how flybys change its velocity (paper). 🤯 Lucy’s flight plan is complex: two gravity assists from Earth (in 2022 and 2024), a flyby of the main-belt asteroid in 2025 (fittingly named Donaldjohanson after the discoverer of the Lucy fossil), arrival at the L4 Trojans in 2027 to study four objects (some of which are binary systems), then another Earth flyby and a slingshot to the L5 Trojans to visit another binary system in 2033. A mission extension is possible beyond 2033 as the spacecraft orbits between the L4 and L5 clouds every six years.