Origin of the discrepancy among water-ice optical-constant datasets

Determine whether the discrepancy in the modeled 3 micrometer water-ice absorption profiles arises from differences in the underlying laboratory measurements and derivation of the optical constants or from the optical-constant datasets representing distinct physical conditions, temperatures, and microphysical states of water ice relevant to astrophysical environments.

Background

The Epoch 1 spectral model fits the observed broad 3 micrometer absorption better when using the Warren water-ice optical constants than when using the low-temperature crystalline-water-ice constants of Mastrapa et al. The paper notes that these datasets produce substantially different band widths and detailed spectral morphologies, creating uncertainty in how the modeled spectra should be physically interpreted.

Resolving whether the discrepancy reflects experimental and derivational differences or genuinely different ice conditions is important because the inferred phase, temperature, aggregate composition, and grain-scale properties of water ice depend sensitively on the adopted optical constants.

References

The origin of this discrepancy remains uncertain, and it is unclear whether it reflects differences in the underlying laboratory measurements and derivation of the optical constants or whether the various datasets capture distinct physical conditions, temperatures, and microphysical states of water ice relevant to astrophysical environments.

— JWST Reveals Refractory-Rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks  (2609.19286 - Protopapa et al., 16 Sep 2026) in Section 2.2, subsection “Epoch 1: Refractory-Rich Water-Ice-Bearing Aggregates”