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Abstract: Hematite is an iron oxide that is very important for the study of climatic evolution of Mars. It can occur in three forms: nanophase (dark purple), fine-grained (red) and coarse-grained (gray). In a previous work, we studied the influence of particle size and shape on the infrared spectra (in the wavelength range 6.25–50μm) of submicron red hematite particles and found that bulk optical constants did not fit the spectra of very fine particles with several classes of models. In the present paper, we derive bulk optical constants of a sample of the same parent material of hematite already used in a previous work in order to determine the particulate optical constants. As a first result we find that, also in this case, bulk and particulate optical constants are different from each other. Furthermore, we show that these bulk optical constants, although derived starting from the same parent material of hematite and used with a model adopting the laboratory measured grain size distribution of the sample, cannot be used to reproduce the spectra of submicron particles. Our results can help the scientific community to appropriately model the contribution of hematite submicron grains to the martian dust for a better understanding of the geologic evolution of the planet. [ABSTRACT FROM AUTHOR]

Abstract: In this work we describe a new method for the derivation of the optical constants of a particulate sample by means of the Hapke theory, starting from directional-hemispherical reflectance measurements. This approach has been applied to calcite fine grains, whose spectra have been obtained in our laboratory in the spectral range . [Copyright &y& Elsevier]

Various indications seem to suggest that in the past the Martian climate allowed the presence of liquid water on the surface of the planet. It is therefore reasonable to think that bodies of standing water were once present in basins such as craters or depressions and that evaporite deposits of sulfates could have formed in these basins. The identification of such deposits, which might have survived in some regions of the planet, could confirm the present hypothesis about the ancient climate on Mars. Recent analyses of Mars spectra, obtained by ground-based observations, show bands consistent with sulfate features. If such data have to be interpreted with the aid of synthetic spectra, the knowledge of the complex refractive index of some sulfate is necessary. In this work we present the optical constants of submicron particles of gypsum (a typical hydrate–sulfate very common on Earth), derived by means of the dispersion theory from transmission spectra. We have performed the calculation of the optical constants in the wavelength range 2–70 μm, also in view of the wide spectral range covered by the Planetary Fourier Spectrometer (PFS) on board of the ESA space mission Mars Express. The data have been compared with optical constants obtained by other authors from reflectance measurements of particulate samples. [Copyright &y& Elsevier]

Theoretical studies and numerical models of the atmosphere and surface of Mars need the knowledge of the optical constants of candidate materials for Martian dust, in a wavelength range as wide as possible. Limestone, as a carbonate-bearing material, is commonly considered a likely component particularly important for its links with the climate evolution and water resources on Mars.In a previous paper, we reported the complex indices of refraction of submicron particles of limestone, derived from laboratory transmission spectra in the wavelength range 3.5–20 μm by means of the dispersion theory. In this work we present the same quantities in a wider spectral range extending from 1.5 up to 62.5 μm. Such an extension is particularly important since limestone, as well as other carbonates, has some of its characteristic features between 20 and 50 μm.Our data are discussed and compared with those given by other authors and obtained with a different method (i.e. reflection measurements) on samples consisting of pressed pellets of randomly oriented calcite grains. As in the case of the previous work, our results point out, again, that the extinction spectra of submicron particles can be better reproduced using optical constants directly obtained in the laboratory for particulate materials.Finally, the extinction and emission properties of limestone grains are used in order to tentatively identify carbonates on Mars and to understand whether these materials are present in the Martian aerosol or on the surface. Our results seem to suggest that, limestone particles can be a minor component of the atmospheric dust rather than of the surface regolith, provided that some bands observed in the Martian spectra will be finally ascribed to such material. [Copyright &y& Elsevier]