Unveiling dark objects in Solar System: grain size effects on the infrared spectrum of mineral
mixtures in presence of opaque components
G. Poggiali1,2, L. Fossi2, A. Wargnier1, J. Beccarelli3, J.B. Brucato2, M.A. Barucci1, P. Beck4, M. Matsuoka5, T. Nakamura6, M.
Pajola3, S. Fornasier1,7, F. Merlin1, A. Doressoundiram1, T. Gautier8 and G. David1
1
LESIA-Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris Cité, 92195 Meudon
Principal Cedex, France (giovanni.poggiali@obspm.fr)
2
INAF-Astrophysical Observatory of Arcetri, Firenze, Italy3
INAF-Astronomical Observatory of Padova, Padova, Italy
4
Institut de Planétologie et d’Astrophysique de Grenoble, OSUG/CNRS, Grenoble, France
5
The Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
6
Department of Geophysics, Tohoku University, Sendai Miyagi, Japan
7
Institut Universitaire de France (IUF), 1 rue Descartes, F-75231 Paris Cedex 05, France,
8
LATMOS, CNRS, Sorbonne Université, Université Versailles St-Quentin, Guyancourt, France
Dark surfaces characterize several bodies in the Solar System: from primitive carbonaceous asteroids to the enigmatic surfaceof Phobos and Deimos, our knowledge on the spectroscopic behaviour of low albedo surfaces is still incomplete. A dark
surface can be related to multiple factors, for example presence of opaque material [1] or strong surface alteration [2]. In order
to interpret remote sensing data, laboratory studies remain a pivotal tool to unveil the surface physical state and composition.
Several processes can be simulated in the laboratory, but the preparation and analysis of complex mixing of analog material isone of the most fundamental tool and, at the same time, one of the most complex study when multiple components are used. In
this work, we aim to study how dark material
mixed with basaltic material at different grain sizes
can affect the spectroscopic features from near- to
mid-infrared (1.25-25 µm).
Our sample set includes four series of basaltic mix(feldspar and pyroxene), at different grain sizes
from < 50 µm to 1000 µm, mixed with amorphous
carbon at increasing weight percentages from 1%
to 50%. We analysed several features on thespectrum of each mineral mixture: (i) near infraredslope; (ii) 2.7 µm OH-stretching band; (iii)
Christiansen features; (iv) Reststrahlen band andTransparency feature. Measurements presented inthis work [3], for the first time take into account alarge wavelength range and point towards a criticaleffect of dark material with a different outcome foreach grain size. Some of the most interesting
results involved the slope and the different
behaviour of the Reststrahlen band. This dataset
will be a good support in the interpretation ofFigure 1. Infrared spectra of basaltic mixtures [BAS] at different grain sizes,
upcoming data from Phobos Martian Moon
<50, 50-200, 200-500 and 500-1000 μm, with addition in different
eXploration mission, as well as in understanding ofproportions,from 1 to 50%, with synthetic amorphous carbon [SAC].
previous data from dark surfaces in the Solar
System like Ryugu and Bennu.
References[1] Cloutis et al 1990, Icarus, 84 (2), 315-333 [2] Hasegawa et al 2022, The Astrophysical Journal Lettes, 939, L9 [3] Poggialiet al 2023, Astronomy & Astrophysics (submitted)