Complex Water Ice Mixtures on NII Nereid: Constraints from NIR Reflectance

We discuss our spectral characterization of the faint Neptunian satellite Nereid from 0.8-2.4 um using the SpeX instrument on the NASA IRTF. We detect spectral absorption features of crystalline water ice in close agreement with previous measurements, but show that models of simple intimate mixtures do not provide complete matches to the observed spectrum. Possible solutions include invoking a more complex continuum, allowing for sub-micron sized grains, and mixtures of both crystalline and amorphous water ice. We show that radiative transfer mixing models that include magnetite and the CM2 chondrite Murchison provide a flexible framework for interpreting spectral variation of icy bodies with neutral-sloped spectra like that of Nereid.