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Reflection, emission, and polarization properties of surfaces made of hyperfine grains, and implications for the nature of primitive small bodies

Sultana, Robin and Poch, Olivier and Beck, Pierre and Schmitt, B. and Quirico, E. and Spadaccia, Stefano and Patty, Lucas and Pommerol, Antoine and Maturilli, Alessandro and Helbert, Jörn and Alemanno, Giulia (2023) Reflection, emission, and polarization properties of surfaces made of hyperfine grains, and implications for the nature of primitive small bodies. Icarus, 395, p. 115492. Elsevier. doi: 10.1016/j.icarus.2023.115492. ISSN 0019-1035.

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Official URL: https://www.sciencedirect.com/science/article/abs/pii/S0019103523000696


Solar System small bodies were the first objects to accrete inside the protoplanetary disk, giving insights into its composition and structure. The P-/D-type asteroids are particularly interesting because of the similarity of their spectra, at visible and near infrared wavelengths (Vis-NIR), with cometary nuclei, suggesting that they are the most primitive types of small bodies. There are various indications that (1) their low albedo in the visible (Vis) and mid-infrared (MIR) wavelength ranges seems mainly controlled by the presence of opaque minerals (iron sulfides, Fesingle bondNi alloys etc.) (Quirico et al., 2016; Rousseau et al., 2018); and (2) their surfaces are made of intimate mixtures of these opaque minerals and other components (silicates, carbonaceous compounds, etc.) in the form of sub-micrometre-sized grains, smaller than the wavelength at which they are observed, so-called “hyperfine” grains. Here, we investigate how the Vis-NIR-MIR (0.55–25 μm) spectral and V-band (0.53 μm) polarimetric properties of surfaces made of hyperfine grains are influenced by the relative abundance of such hyperfine materials, having strongly different optical indexes. Mixtures of grains of olivine and iron sulfide (or anthracite), as analogues of silicates and opaque minerals present on small bodies, were prepared at different proportions. The measurements reveal that these mixtures of hyperfine grains have spectral and polarimetric Vis-NIR properties varying in strongly nonlinear ways. When present at even a few percent, opaque components dominate the Vis-NIR spectral and polarimetric properties, and mask the silicate bands at these wavelengths. The Vis-NIR spectral slope ranges from red (positive slope), for pure opaque material, to blue (negative slope) as the proportion of silicates increases, which is reminiscent of the range of spectral slopes observed on P/D/X/C- and B-types asteroids. The spectra of the darkest mixtures in the Vis-NIR exhibit the absorption bands of Sisingle bondO in olivine around 10 μm in the MIR, which is observed in emission for several small bodies. The samples studied here have macro- and micro-porosities lower than 78%, indicating that surfaces more compact than “fairy castle” hyperporous (80–99%) ones can also exhibit a blue spectral slope or a silicate signature at 10 μm. Remarkably, some mixtures exhibit altogether a red spectral slope in the Vis-NIR, a 10-μm feature in the MIR, and a V-band polarimetric phase curve similar (but not identical) to P-/D-type asteroids, reinforcing the hypothesis that these bodies are made of powdery mixtures of sub-micrometre-sized grains having contrasted optical indexes. This work shows that both the contrasted optical indexes of the components, and the dispersion or aggregation −depending on their relative proportions− of their hyperfine grains, induce different light scattering regimes in the Vis-NIR and MIR, as observed for primitive small bodies. The optical separation of hyperfine grains seems to be a major parameter controlling the optical properties of these objects.

Item URL in elib:https://elib.dlr.de/195659/
Document Type:Article
Title:Reflection, emission, and polarization properties of surfaces made of hyperfine grains, and implications for the nature of primitive small bodies
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Sultana, RobinUniv. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, FranceUNSPECIFIEDUNSPECIFIED
Poch, OlivierLISA, UMR CNRS 7583, Université Paris Est Créteil et Université Paris Diderot, Institut Pierre Simon Laplace, 61, av du Général de Gaulle, 94010, Créteil Cedex, FranceUNSPECIFIEDUNSPECIFIED
Beck, PierreUniv. Grenoble Alpes, CNRS - Centre National de la Recherche Scientifique, IPAG, Grenoble,UNSPECIFIEDUNSPECIFIED
Schmitt, B.Université Grenoble Alpes, IPAG, GrenobleUNSPECIFIEDUNSPECIFIED
Quirico, E.Grenoble Planetology LaboratoryUNSPECIFIEDUNSPECIFIED
Spadaccia, StefanoGrenoble Planetology LaboratoryUNSPECIFIEDUNSPECIFIED
Patty, LucasGrenoble Planetology LaboratoryUNSPECIFIEDUNSPECIFIED
Pommerol, AntoineGrenoble Planetology LaboratoryUNSPECIFIEDUNSPECIFIED
Maturilli, AlessandroUNSPECIFIEDhttps://orcid.org/0000-0003-4613-9799UNSPECIFIED
Helbert, JörnUNSPECIFIEDhttps://orcid.org/0000-0001-5346-9505UNSPECIFIED
Date:17 February 2023
Journal or Publication Title:Icarus
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:p. 115492
Keywords:asteroids, small bodies, spectroscopy
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Project BepiColombo - MERTIS and BELA, R - Project MMX - miniRad and Science
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Laboratories
Deposited By: Helbert, Dr.rer.nat. Jörn
Deposited On:27 Jun 2023 10:38
Last Modified:19 Oct 2023 15:11

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