Carbon and Space Weathering: Mie-modified Hapke Spectral Modeling with Submicroscopic Carbon

The radiative transfer model of Hapke [1,2] can be used to predict the bidirectional reflectance spectra in a forward modeling approach. Hapke [2] applied Maxwell-Garnett equivalent theory to combine optical properties of Fe⁰ with those of host lunar materials to successfully produce the observed reddening and darkening caused by the submicroscopic iron (smFe⁰). Although this works for the smallest smFe⁰ particles (<100 microns), for larger particles (50-3000 nm) the model matches the slopes and albedos only at the longer wavelengths but fails to reproduce the spectrum at shorter wavelengths [3]. To address this, Lucey and Riner [4] used Mie theory to include the effects of larger smFe⁰ particles. For the purpose of the Moon, Fe⁰ is the dominant submicroscopic phase; however, for carbon-rich bodies, carbon may be the dominant space-weathering product [5]. Therefore, we have adapted spectral models to include amorphous carbon as a possible space weathering component (smC) and will compare and contrast the spectral differences. [1] Hapke (1981) JGR, 86, 3039-3054. [2] Hapke (2012), Theory of Reflectance and Emittance Spectroscopy, 2nd ed., Cambridge University Press, New York. [3] Lucey & Noble (2008) Icarus, 197(1), 348-353. [4] Lucey & Riner (2011) Icarus, 212, 451-462. [5] Trang et al. (2017) Icarus, 293, 206-17.

The radiative transfer model of Hapke [1,2] can be used to predict the bidirectional reflectance spectra in a forward modeling approach. Hapke [2] applied Maxwell-Garnett equivalent theory to combine optical properties of Fe⁰ with those of host lunar materials to successfully produce the observed reddening and darkening caused by the submicroscopic iron (smFe⁰). Although this works for the smallest smFe⁰ particles (<100 microns), for larger particles the model matches the slopes and albedos only at the longer wavelengths but fails to reproduce the spectrum at shorter wavelengths [3]. To address this, Lucey and Riner [4] used Mie theory to include the effects of larger smFe⁰ particles (50-3000 nm). For the purpose of the Moon, Fe⁰ is the dominant submicroscopic phase; however, for carbon-rich bodies, carbon may be the dominant space-weathering product [5]. Therefore, we have adapted spectral models to include amorphous carbon as a possible space weathering component (smC) and will compare and contrast the spectral differences. [1] Hapke (1981) JGR, 86, 3039-3054. [2] Hapke (2001) JGR, 106, 10,039-10,073. [3] Lucey & Noble (2008) Icarus, 197(1), 348-353. [4] Lucey & Riner (2011) Icarus, 212, 451-462. [5] Trang et al. (2017) Icarus, 293, 206-17.