http://arxiv.org/abs/2204.04192
Widespread detection of amorphous and crystalline water (H${}{2}$O) ice in the outer solar system bodies and the interstellar medium has been confirmed over the past decades. Radiative transfer models (RTMs) are used to estimate the grain sizes of H${}{2}$O ice from near-infrared (NIR) wavelengths. Wide discrepancies in the estimation of H${}{2}$O ice grain size on the Saturnian moons (Hansen, 2009), as well as nitrogen (N${}{2}$) and methane (CH${}{4}$) ices on Kuiper belt objects have been reported owing to different scattering models used (Emran and Chevrier, 2022). We assess the discrepancy in the grain size estimation of H${}{2}$O ice at a temperature of 15, 40, 60, and 80 K (amorphous) and 20, 40, 60, and 80 K (crystalline) – relevant to the outer solar system and beyond. We compare the single scattering albedos of H${}{2}$O ice phases using the Mie theory (Mie, 1908) and Hapke approximation models (Hapke, 1993) from the optical constant at NIR wavelengths (1 – 5 $\mu$m). This study reveals that the Hapke approximation models – Hapke slab and internal scattering model (ISM) – predict grain size of the crystalline phase, overall, much better compared to the amorphous phase at temperatures of 15 – 80 K. However, the Hapke slab model estimates much approximate grain sizes, in general, to that of the Mie model’s prediction while ISM exhibits a higher uncertainty. We recommend using the Mie model for unknown spectra of outer solar system bodies and beyond in estimating H${}{2}$O ice grain sizes. While choosing the approximation model for employing RTMs, we recommend using a Hapke slab approximation model over the internal scattering model.
A. Emran and V. Chevrier
Mon, 11 Apr 22
44/61
Comments: 15 pages, 4 figures, 2 tables
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