The NASA Lucy Mission: Surveying the Diversity of Trojan Asteroids

The Lucy Mission is a NASA Discovery class mission to send a highly capable and robust spacecraft to investigate seven Jupiter Trojan asteroids; a class of stable, primitive bodies near both the L4 and L5 Lagrange points with Jupiter. It is believed that Jupiter Trojan asteroids are leftover planetesimals from the outer planetary system that have been preserved since early in Solar System history, and represent the last of all of the stable populations of the Solar System to be visited by spacecraft.

Lucy is slated to launch in October 2021, reach its first Trojan asteroid in 2027, and have its final encounter in 2033. During its lifetime, Lucy will perform five Trojan encounters closely studying at least seven objects (one encounter is of a nearly equal mass binary and another is an asteroid with a known satellite). The science goals include determining the surface composition, assessing the geology, determining the bulk properties and searching for satellites around all of Lucy’s targets. The payload suite consists of a color camera and infrared imaging spectrometer, a high resolution panchromatic imager, and a thermal infrared spectrometer. Additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras and the telecommunication subsystem to measure the mass of the Trojan asteroids.

Lucy’s Trojan targets include one C-type (Eurybates, 64 km in diameter), three P-types (Menoetius, Patroclus, and Polymele; 105, 114, 21 km in diameter, respectively), and two D-types (Leucus and Orus; 41 and 52 km in diameter, respectively), thereby covering a wide range of spectral types and sizes. Lucy will be the first spacecraft to observe the largest remnant of a catastrophic collision up close (Eurybates), and the first to visit a near-equal mass binary (Patroclus and Menoetius). In addition, on its way to L4, Lucy will fly by DonaldJohanson in 2025, a 4 km in diameter Main Belt asteroid named in honor of the discoverer of the Lucy fossil. In this talk, recent results from an international observational campaign of some of the Lucy’s targets will be presented, including the detection of a small satellite (1-2 km) orbiting Eurybates, and a detailed characterization of Leucus’s shape and rotational axis orientation.