Thermophysical modeling of (15) Eunomia from high-resolution ALMA data

Thermophysical properties such as thermal inertia can be used to understand the regolith properties and surface compositions of asteroids, from which we can infer the nature and evolutionary processes occurring on the underlying body. We have used a thermophysical model to derive the global values of thermal inertia, dielectric constant and millimeter emissivity of (15) Eunomia, which is the largest S-type asteroid. The best-fit values for these parameters were constrained by 1.3 mm thermal emission data acquired in 2019 by the Atacama Large Millimeter/submillimeter Array (ALMA) at 33 km resolution. ALMA is able to spatially resolve asteroids at millimeter wavelengths that are sensitive to thermal emission from the subsurface beyond the heavily weathered surface. The thermophysical model we have used is based on Delbo et al. (2015), and adapted to take into account the spatially resolved thermal emission data including subsurface emission (de Kleer et al. 2021; Cambioni et al. 2022). Compared to disk integrated observations, spatially resolved thermal emission data allows for the spatial variations in thermal properties to be investigated, enabling a better understanding of surface/subsurface heterogeneity. We will present results of our thermophysical model of Eunomia and compare with the results of Psyche obtained using the same observational and modeling approach (de Kleer et al. 2021), to interpret the implications on Eunomia’s surface thermophysical properties. References: Delbo et al. 2015, Asteroids IV 107. de Kleer et al. 2021, PSJ 2, 4, id. 149. Cambioni et al. 2022, JGR: Planets, 127, 6, id. e07091.