Spectral Mixture Modeling with Laboratory Near-Infrared Data I: Insights into Compositional Analysis of Europa

Europa's surface composition and physical characteristics are commonly constrained using spectral deconvolution through linear mixture (LM) modeling and radiative transfer–based (RT) intimate mixture modeling. Here, I compared the results of these two spectral modeling— LM versus RT— against laboratory spectra of water (H2O) ice and sulfuric acid octahydrate (H2SO4·8H2O) mixtures measured at near-infrared wavelengths (1.2–2.5 µm) with grain sizes of 90–106 µm (Hayes & Li, 2025). The modeled abundances indicate that the RT more closely reproduces the laboratory abundances, with deviations within ±5% for both H2O ice and H2SO4·8H2O with ~100 µm grains. In contrast, the LM shows slightly larger discrepancies, typically ranging from ±5-15% from the true abundances. Interestingly, the RT tends to underestimate the abundance of H2SO4·8H2O and overestimate H2O ice, whereas the LM shows the opposite trend across all mixtures. Nonetheless, when H2SO4·8H2O either dominates (>80% as observed on Europa’s trailing hemisphere; Carlson et al. 2005) or is present only in trace amounts (~10% on areas in Europa’s leading hemisphere; Dalton et al. 2013; Ligier et al. 2016), both the LM and RT render acceptable results within ±10% uncertainty. Thus, spectral modeling using the RT is preferred for constraining the surface composition across Europa, although the LM remains viable in specific compositional regimes.