Lucy will be the first space mission to explore a population of small bodies known as the Trojans. The Trojans are outer Solar System asteroids that orbit the Sun “in front of” and “behind” the gas giant Jupiter, at the same distance from the Sun as Jupiter. The gas giant is massive enough that normally it scatters away all asteroids in its vicinity, but, due to the combined gravitational influences of the Sun and Jupiter, these Trojan asteroids have been trapped on stable orbits (around what is known as the Lagrange Points) for billions of years. These Trojans provide a unique, never-before-explored sample of the remnants of our early Solar System.
Planet formation and evolution models suggest that the Trojan asteroids are likely remnant of the same primordial material that formed the outer planets, and thus serve as time capsules from the birth of our Solar System over 4 billion years ago. These primitive bodies hold vital clues to deciphering the history of our Solar System and may even tell us about the origins of organic materials—and even life—on Earth.
The Lucy mission is named after the fossilized skeleton of an early hominid found in Ethiopia on Nov 24, 1974 by Donald Johanson and Tom Gray. That Lucy in turn was named by expedition member Pamela Alderman after a celebratory evening dancing and singing to the Beatles’ song “Lucy in the Sky With Diamonds.” Just as that Lucy fossil provided unique insights into humanity’s evolution, the Lucy mission promises to revolutionize our knowledge of planetary origins and the formation of the Solar System.
Lucy will fly by and carry out remote sensing on eight different Trojan asteroids during five flybies to address the following science objectives:
Surface Geology - Lucy will map the albedo, shape, crater spatial and size-frequency distributions, determine the nature of crustal structure and layering, and determine the relative ages of surface units.
Surface Color and Composition - Lucy will map the color, composition and regolith properties of the surface of the Trojan asteroid and determine the distribution of minerals, ices, and organic species.
Interiors and Bulk Properties - Lucy will determine the masses and densities, and study sub-surface composition via excavation by craters, fractures, ejecta blankets, and exposed bedding.
Satellites and Rings - Lucy will look for rings and satellites of the Trojan asteroids.