2021/05/24 by Katherine de Kleer, de Kleer, Katherine, Saverio Cambioni +3 · 2 citations
Physics and Astronomy · #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #astro-ph.EP
paper · pdf · doi:10.48550/arxiv.2105.11372
To be published in Planetary Science Journal
arxiv created 2021/05/24 · arxiv updated 2021/05/25
The asteroid (16) Psyche is the largest of the M-type asteroids, which have been hypothesized to be the cores of disrupted planetesimals and the parent bodies of the iron meteorites. While recent evidence has collected against a pure metal composition for Psyche, its spectrum and radar properties remain anomalous. We observed (16) Psyche in thermal emission with the Atacama Large (sub-)Millimeter Array (ALMA) at a resolution of 30 km over 2/3 of its rotation. The diurnal temperature variations are at the ∼10 K level over most of the surface and are best fit by a smooth surface with a thermal inertia of 280±100 J m-2 K-1 s-1/2. We measure a millimeter emissivity of 0.61±0.02, which we interpret via a model that treats the surface as a porous mixture of silicates and metals, where the latter may take the form of iron sulfides/oxides or alternatively as conducting metallic inclusions. The emissivity indicates a metal content of no less than 20% and potentially much higher, but the polarized emission that should be present for a surface with ≥20% metal content is almost completely absent. This requires a highly scattering surface, which may be due to the presence of reflective metallic inclusions. If such is the case, a consequence is that metal-rich asteroids may produce less polarized emission than metal-poor asteroids, exactly the opposite prediction from standard theory, arising from the dominance of scattering over the bulk material properties.