The complex refractive index of limestone particles: an extension to the FIR range for Mars applications

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. revious 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. ta 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. y, 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.