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The Surface of (16) Psyche from Thermal Emission and Polarization Mapping

de Kleer, Katherine and Cambioni, Saverio and Shepard, Michael (2021) The Surface of (16) Psyche from Thermal Emission and Polarization Mapping. Planetary Science Journal, 2 (4). Art. No. 149. ISSN 2632-3338. doi:10.3847/PSJ/ac01ec.

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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 Millimeter/submillimeter Array at a resolution of 30 km over two-thirds 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, 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.

Item Type:Article
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URLURL TypeDescription Paper
de Kleer, Katherine0000-0002-9068-3428
Cambioni, Saverio0000-0001-6294-4523
Shepard, Michael0000-0002-8441-2488
Additional Information:© 2021. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 March 11; revised 2021 May 5; accepted 2021 May 7; published 2021 August 5. The authors are grateful to the NRAO and Melissa Hoffman, Erica Keller, and Tony Remijan at the North American ALMA Science Center (NAASC) for their support in calibrating and imaging the ALMA data through a PI data reduction visit. K.d.K. thanks Bryan Butler, Arielle Moullet, and Mike Brown. S.C. thanks Guy Consolmagno and Robert Macke at the Vatican Observatory for discussion about the thermophysical nature of Psyche's meteorite analogs and Marco Delbo at the Observatoire de la Côte d'Azur for technical support with the thermophysical model. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.01271.S. ALMA is a partnership of the ESO (representing its member states), NSF (USA), and NINS (Japan), together with the NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Group:Astronomy Department
Subject Keywords:Solar system; Solar system astronomy; Asteroids; Asteroid surfaces; Small Solar System bodies; Radio interferometry
Issue or Number:4
Classification Code:Unified Astronomy Thesaurus concepts: Solar system (1528); Solar system astronomy (1529); Asteroids (72); Asteroid surfaces (2209); Small Solar System bodies (1469); Radio interferometry (1346)
Record Number:CaltechAUTHORS:20210603-122530519
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Official Citation:Katherine de Kleer et al 2021 Planet. Sci. J. 2 149
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109369
Deposited By: George Porter
Deposited On:03 Jun 2021 21:50
Last Modified:05 Aug 2021 21:51

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