Discrepancy in grain size estimation of H2O ice in the outer solar system and the interstellar medium.

by Emran, A.; Chevrier, V. F.

Widespread detection of amorphous and cryst. water (H2O) 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 est. the grain sizes of H2O ice from near-IR (NIR) wavelengths. Wide discrepancies in the estn. of H2O ice grain size on the Saturnian moons, as well as nitrogen (N2) and methane (CH4) ices on Kuiper belt objects have been reported owing to different scattering models used. We assess the discrepancy in the grain size estn. of H2O ice at a temp. of 15, 40, 60, and 80 K (amorphous) and 20, 40, 60, and 80 K (cryst.) - relevant to the outer solar system and beyond. We compare the single scattering albedos of H2O ice phases using the Mie theory and Hapke approxn. models from the optical const. at NIR wavelengths (1 - 5 µm). This study reveals that the Hapke approxn. models - Hapke slab and internal scattering model (ISM) - predict grain size of the cryst. phase, overall, much better compared to the amorphous phase at temps. of 15 - 80 K. However, the Hapke slab model ests. much approx. 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 estg. H2O ice grain sizes. While choosing the approxn. model for employing RTMs, we recommend using a Hapke slab approxn. model over the internal scattering model.

arXiv.org, e-Print Archive, Astrophysics
Start Page