In 1974, paleoanthropologist Donald Johanson unearthed fragments of a fossilized Australopithecus skeleton from Ethiopian soil, which he used to theorize evolutionary connections between early primates and later humans. The remains were christened Lucy, after the popular Beatles classic “Lucy in the Sky with Diamonds”. Forty-seven years later, NASA launched a namesake mission into the heavens, to seek clues of planetary evolution within our Solar System.
NASA’s Lucy is a probe roughly 52 feet wide, weighing just over 3400 pounds. Equipped with several visible light, infrared, and radio sensors, Lucy will study the physical and chemical nature of several asteroids in Jupiter’s orbit. It is currently beginning an unusual trajectory involving three Earth flybys over the next few years. Eventually, it will settle into a stable, double figure-eight orbit between Earth and Jupiter.
Most asteroids inhabit a main belt between Mars and Jupiter, but nearly as many also occupy the L4 and L5 points of Jupiter’s orbit. These are special locations where the gravitational influence of Jupiter and Sun are counterbalanced. Stray asteroids have congregated at these spots, co-orbiting the Sun with Jupiter. The L4/L5 groups are respectively called the “Greek” and “Trojan” camps, after the opposing sides of the Trojan war memorialized in Homer’s The Iliad. Lucy will directly study five members-- four (Eurybates, Polymele, Leucus, and Orus) in the Greek camp, and one (Patroclus, with its tiny satellite Menoetius) in the Trojan camp.
These asteroidal retinues intrigue scientists for two reasons. Earthbound observations suggest that many members contain organic-rich silicates, with possible subsurface water ice. Lucy may extend our understanding of how biologically interesting compounds arose in the Solar System. Observations also suggest that several members are pieces of larger masses; thus, Lucy may also help refine theories of how planetary bodies form, collide, fragment, and migrate.
Before entering the Greek camp, Lucy will visit asteroid DonaldJohanson in the main belt, believed to have been sheared from the larger asteroid Erigone. While there for the science, Lucy’s presence will poetically pay homage to its terrestrial namesake.
Indeed, Lucy may pay respects in a second way. Its final orbit has a theoretical duration of tens of millennia. On the chance that our distant descendants might retrieve Lucy, the probe carries a gold plaque inscribed with philosophical messages. One of these comes from John Lennon, principal lyricist of “Lucy in the Sky with Diamonds”:
A dream you dream alone is only a dream.
A dream you dream together is reality.
Western Slope Skies is produced by the Black Canyon Astronomical Society and KVNF Community Radio. This episode was written and voiced by Michael T. Williams.