PREDICTIVE CONSTRAINTS ON THE CORE EVOLUTION OF (16) PSYCHE USING ITS TECTONICS AND MOMENT OF INERTIA

Radial contraction has historically been used to infer a planetary body’s thermal history based on surface observations of pervasive thrust faulting [e.g., 1–3]. Additionally, the measured moment of inertia (MOI) of a body can be determined from a low-degree gravity investigation and can provide non-unique constraints on the interior structure [e.g., 4]. As we look forward to the Psyche mission’s arrival in 2029, predictive modeling efforts focused on Psyche’s tectonic history and MOI are crucial to the interpretation of the mission’s planned observations and measurements.

To model the thermal evolution of a differentiated Psyche we use a 1-D finite difference model of thermal conduction coupled with solidification of an isothermal fluid core as described in [5] with the addition of sulfur to our modeled cores. To determine the radial contraction history for our models, we include radial changes due to thermal contraction in addition to the volume change due to the phase change from liquid to solid iron within the core. The methods that drive our calculations are described in [1]. Additionally, we calculate the principal MOI factor, C/MR², for each of our models under the assumption of spherical symmetry.

Our models include a range of silicate layer thicknesses (1 – 50 km), initial core sulfur contents (0 – 10 wt.%), and inward and outward directions of core growth. We generally find that increasing the thickness of the outer silicate layer by 10 km results in a ~1-km reduction in total radial contraction. Additionally, the timing of full core solidification, and thus a large amount of predicted contraction, can differ by up to 25 Myr for inward vs outward core growth. Finally, our calculated MOI factors for models with an iron-sulfur core and inward core growth are consistently larger than those with outward core growth. Overall, spacecraft-derived estimates of Psyche’s MOI [e.g., 6] and global contraction can be used to place constraints on Psyche’s silicate mass fraction and determine the direction of core solidification.

References: [1] Solomon, S. C. (1977) Physics of the Earth and Planetary Interiors, 15, 135–145. [2] Byrne, P. K. et al. (2014) Nature Geosci, 7, 301–307. [3] Watters, T. R. (2021) Commun Earth Environ, 2, 1–9. [4] Vaillant, T. et al. (2019) A&A, 622, A95. [5] Nichols-Fleming, F. et al. (2023) 54th LPSC, 2806. [6] Zuber, M. T. et al. (2022) Space Sci Rev, 218, 57.