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

Abstract

There are various indications that the most primitive small bodies (P, D-type asteroids, comets) have surfaces made of intimate mixtures of 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 spectral and V-band 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 Si-O in olivine around 10 m in the MIR, which is observed in emission for several small bodies. 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.

arXiv commentaccepted in Icarus

References in corpus (27)

• The taxonomic distribution of asteroids from multi-filter all-sky photometric surveys
• Spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from the OSIRIS instrument onboard the ROSETTA spacecraft
• Retrieving the Aerosol Complex Refractive Index using PyMieScatt: A Mie Computational Package with Visualization Capabilities
• Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids
• Synthesis of the Morphological Description of Cometary Dust at Comet 67P
• Near-Infrared Spectroscopy of Trojan Asteroids: Evidence for Two Compositional Groups
• Near-infrared absorption properties of oxygen-rich stardust analogues: The influence of coloring metal ions
• Explosion of Comet 17P/Holmes as revealed by the Spitzer Space Telescope
• Multiple Asteroid Systems: Dimensions and Thermal Properties from Spitzer Space Telescope and Ground-Based Observations
• Dust of comet 67P/Churyumov-Gerasimenko collected by Rosetta/MIDAS: classification and extension to the nanometre scale
• Different origins or different evolutions? Decoding the spectral diversity among C-type asteroids
• Infrared detection of aliphatic organics on a cometary nucleus
• SHADOWS: a spectro-gonio radiometer for bidirectional reflectance studies of dark meteorites and terrestrial analogs: design, calibrations, and performances on challenging surfaces
• Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-μm sized cosmochemical analogues
• Mid-infrared spectra of comet nuclei
• Polarimetry of Water Ice Particles Providing Insights on Grain Size and Degree of Sintering on Icy Planetary Surfaces
• Linear spectro-polarimetry: a new diagnostic tool for the classification and characterisation of asteroids
• Are Large Trojan Asteroids Salty? An Observational, Theoretical, and Experimental Study
• Rotationally-Resolved Spectroscopic Characterization of near-Earth object (3200) Phaethon
• Water abundance at the surface of C-complex main-belt asteroids
• How Many Hydrated NEOs Are There?
• Visible and near-infrared reflectance of hyperfine and hyperporous particulate surfaces
• Close-up images of the final Philae landing site on comet 67P/Churyumov-Gerasimenko acquired by the ROLIS camera
• A Possible Explanation for the Blue Spectral Slope Observed on B-type Asteroids
• Broadband Linear Polarization of Jupiter Trojans
• Origins of colors variability among C-cluster main-belt asteroids
• Negative polarization properties of regolith simulants -- Systematic experimental evaluation of composition effects

Cited by in corpus (4)

• Composition and thermal properties of Ganymede's surface from JWST/NIRSpec and MIRI observations
• Comparative Mid-Infrared Spectroscopy of Dark, Primitive Asteroids: Does Shared Taxonomic Class Indicate Shared Silicate Composition?
• Optical spectropolarimetry of large C-complex asteroids: polarimetric evidence for heterogeneous surface compositions
• Quantitative grain size estimation on airless bodies from the negative polarization branch. I. Insights from experiments and lunar observations