Among the five finalists for NASA’s Discovery program, I had become attached to the Near Earth Object Camera (NEOCam), whose purpose was to expand our catalog greatly, with the potential, according to mission backers, of finding ten times more NEOs than we’ve found to date. We’ll see if NEOCam has a future (I’ve just learned that it has been given extended funding for an additional year by NASA), but for now NASA has announced two other Discovery-class missions, both of which have objectives among the asteroids.

Lucy, scheduled for a launch in the fall of 2021, is to be a robotic mission with the goal of exploring six of the Jupiter Trojan asteroids. The Trojans share Jupiter’s orbit while moving swarm-like around the planet’s L4 and L5 Lagrangian points. Over 6000 Jupiter Trojans are now known, but the population is thought to be vast, with as many as 1 million Trojans larger than 1 kilometer in diameter. As to their origin, there is much to learn. They may be captured asteroids or comets, or as this short NASA video explains, even Kuiper Belt Objects.

From the standpoint of Solar System evolution, the Trojans make for interesting science. They’re relics of the primordial material of the outer system, and I see that principal investigator Harold F. Levison cites the mission’s name in connection with another Lucy, the fossil fragments that have been so significant in our understanding of human development. We’ll see if this Lucy gets as much public attention as its namesake, which acquired its name from the Beatles song ‘Lucy in the Sky with Diamonds,’ played at the recovery site in Ethiopia. Breaking out the Sgt. Pepper album on this Lucy’s arrival at its first target seems a natural.

There are connections between the Lucy effort and the highly successful New Horizons mission, in the form of later versions of the familiar RALPH and LORRI science instruments, and evidently several members of the Lucy mission team are connected with New Horizons as well. Lucy also benefits from the contributions of several members of the OSIRIS-REx team, the latter a robotic spacecraft now on its way to rendezvous with asteroid Bennu.


Image: (Left) An artist’s conception of the Lucy spacecraft flying by the Trojan Eurybates – one of the six diverse and scientifically important Trojans to be studied. Trojans are fossils of planet formation and so will supply important clues to the earliest history of the solar system. (Right) Psyche, the first mission to the metal world 16 Psyche will map features, structure, composition, and magnetic field, and examine a landscape unlike anything explored before. Psyche will teach us about the hidden cores of the Earth, Mars, Mercury and Venus.
Credit: SwRI and SSL/Peter Rubin.

The other mission is Psyche, dedicated to a single asteroid of that name that appears to be the survivor of an early collision with another object that violently disrupted a protoplanet. About 210 kilometers in diameter, 16 Psyche is thought to be composed mostly of metallic iron and nickel, a composition similar to the Earth’s core. We seem to be looking at what would have become the core of a Mars-sized planet, now without its outer rocky layers. Thomas H. Prettyman, a co-investigator on the Psyche mission, explains:

“Psyche is thought to be the exposed core of a planetary embryo – perhaps like Vesta – that initially melted and later cooled to form a central metallic core, silicate mantle, and basaltic crust. The outer layers may have been removed in a violent collision, leaving the core exposed. Psyche will provide a close-up look at a planetary core, providing new insights into the evolution and inner workings of terrestrial planets.”

The robotic Psyche mission will launch in the fall of 2023, with arrival at 16 Psyche in 2030 after two gravity assists, one from an Earth flyby, the second from a flyby of Mars. Both missions have this is common: They target the development of the early Solar System, one by observing the remnants of formation among the Jupiter Trojans, the other by seeing the interior of what might have become a planet. Let’s hope for the kind of success for both that we saw in earlier Discovery missions like MESSENGER and Dawn. OSIRIS-REx, meanwhile, is on course for a 2018 rendezvous with asteroid Bennu, with sample return to follow.