The latest NASA mission is called Lucy. It is named in honor of the hominid Lucy, and its goal is the study of Trojan asteroids, which will reveal information about planet formation, as they are remnants of the materials that aggregated during the early stages of the Solar System‘s formation of celestial bodies. The Australopithecus was itself named after a song by the Beatles, Lucy in The Sky with Diamond which the researchers were listening to at that precise moment in 1977.
The mission is part of NASA’s esteemed Discovery program. This program gives scientists the opportunity to delve deep into their imagination and find new ways to uncover the mysteries of our solar system. Since 1992, the program has marked a breakthrough in how NASA explores space. Its purpose is to deepen human understanding of the solar system by exploring planets, their moons, and small bodies such as comets and asteroids.
These particular asteroids are true time capsules dating back to the birth of our Solar System over 4 billion years ago. The swarm of Trojan asteroids is associated with the planet Jupiter. Captured by its enormous gravity, they are remnants of the primordial material that formed the outer planets. The Trojans orbit the Sun in two loose groups. One group precedes Jupiter in its path, the other follows it by 60° in its orbit.
Enclosed around the two Lagrange points equidistant from the Sun and Jupiter, the Trojans are stabilized by the Sun and its largest planet in an act of gravitational balance. Lucy will be the first space mission to study these asteroids. The mission is named after the fossilized human ancestor (called Lucy by its discoverers) whose skeleton provided a unique insight into the evolution of humanity. Similarly, the Lucy mission will revolutionize our understanding of planetary origins and the formation of the solar system.
Lucy was launched on October 16, 2021, and with the help of Earth‘s gravity, will complete a 12-year journey to eight different asteroids, one asteroid from the main belt and seven Trojan. Lucy’s complex path will bring it close to the two groups of Trojans and give us our first close-up view of all three major types of bodies in the swarms.
The P and D-type Trojans resemble those found in the Kuiper Belt of icy bodies that extend beyond Neptune‘s orbit. The C-types are mainly found in the outer parts of the main asteroid belt, between Mars and Jupiter. All Trojans are believed to be rich in dark carbon compounds. Under an insulating blanket of dust, they are likely rich in water and other volatile substances.
This diagram illustrates Lucy’s orbital path. The spacecraft’s path (green) is shown in a reference frame where Jupiter remains stationary. After the October 2021 launch, Lucy has two close passes of Earth before reaching its targets. Between 2027 and 2028, the spacecraft will pass through the L4 cloud, flying close to Eurybates (white), Polymele (pink), Leucus (red), and Orus (red). After looping back toward Earth, Lucy will visit the L5 cloud and encounter the Patroclus-Menoetius binary (pink) in 2033. As a bonus, in 2025 on the way to L4, Lucy will fly close to a small main belt asteroid, Donaldjohanson.
Lucy will perform flybys with remote sensing on seven different Trojan asteroids to address numerous scientific goals. First, it will study their geology. By mapping albedo, shape, spatial distribution of craters, and size-frequency distribution, it will determine the nature of the structure and crustal layering and ascertain the relative ages of surface units.
Lucy will map the color, composition, and properties of the asteroids’ surface regolith and determine the distribution of minerals, ices, and organic species. It will also calculate masses and densities by studying subsurface composition through crater excavations, fractures, and blanket materials.
Lucy will measure over 14 meters from tip to tip. Most of this size is due to the enormous solar panels (each over 7 meters in diameter). These are necessary to power the spacecraft as it flies toward Jupiter’s orbit. Lucy’s Instrument Pointing Platform (IPP) will carry four instruments for remote sensing science.
RALPH is the multispectral color camera for visible imaging and the Linear Etalon Imaging Spectral Array (LEISA) infrared imaging spectrometer. LEISA will allow us to search for absorption lines that serve as fingerprints for various silicates, ices, and organic substances likely to be found on the surface of the Trojan asteroids.
LORRI, the Long Range Reconnaissance Imager, is the high-resolution visible spatial camera. This camera will provide the most detailed images of the asteroids’ surface.
TESS is the thermal emission spectrometer. This infrared spectrometer will allow Lucy’s team to learn much more about the Trojans’ properties, including their thermal inertia, how well the bodies retain heat. All of this will allow for the understanding of the composition and structure of material on the asteroids’ surfaces.
Additionally, Lucy will use its high-gain antenna to determine the masses of the targets using the Doppler shift of the radio signal. Lucy will also use its Terminal Tracking Camera (T2CAM) to capture wide-field images of the asteroids to better constrain the shapes of the asteroids.