SPACE EXPLORATION OF PRIMITIVE AND METALLIC ASTEROIDS: A SCIENTIFIC RATIONALE FOR THE NASA LUCY AND PSYCHE MISSIONS (Invited Presentation)

Spacecraft have roamed far and wide across the Solar System, passing by numerous small bodies from the orbit of the Earth to beyond the orbit of Pluto. New NASA Discovery missions are bound to expand our knowledge by visiting two classes of asteroids never seen before at close range.

The Lucy mission will accomplish the first reconnaissance of the Trojan asteroids (Levison et al. 2021), a population of primitive asteroids—estimated to contain more than a million objects larger than 1 km in diameter—, which lead and trail Jupiter by 60° along its orbit around the Sun. Lucy’s trajectory has been carefully designed to target some of the most scientifically intriguing Trojan asteroids: Eurybates–Queta, Polymele, Leucus, Orus, Patroclus–Menoetius. The first Trojan asteroid the Lucy spacecraft will encounter is the 60-km Eurybates, the largest remnant of a parent body that was disrupted by a violent collision, and the final flyby will be of a near equal-size binary pair, Patroclus and Menoetius (~120 and ~110 km, respectively), among the largest Trojan asteroids.

The Psyche mission will explore the 225-km Main Belt asteroid Psyche, a likely metal-rich object. The current best interpretation of available data suggests that Psyche may have 30-60 vol.% metal (Elkins-Tanton et al. 2020). This conclusion primarily rests on latest mass and volume estimates combined with radar, spectral and thermal inertia observations. Psyche may be dominantly metallic (Fe-Ni alloys), but it could contain up to 60% porosity to explain the current best estimate of Psyche’ density (~3.7-4.1 g/cc). Alternatively, Psyche could be an assemblage made dominantly of Fe-Ni with low-Fe silicates, sulfides, and some porosity (Elkins-Tanton et al. 2020).

In this talk, I will discuss the scientific objectives of both Lucy and Psyche missions, including our current understanding of the physical properties of their targets based on recent ground-based observations and laboratory experiments.

Levison H., et al. Lucy Mission to the Trojan Asteroids: Science Goals. The Planetary Science Journal, 2:171, 2021.

Elkins-Tanton L., et al. Observations, meteorites, and models: A pre-flight assessment of the composition and formation of (16) Psyche. Journal of Geophysical Research: Planets, 125, 2020.