Spectral Decomposition Reveals Surface Processes on Europa

Abstract

Competing processes shape Europa's surface: geological activity replenishes material through resurfacing, while bombardment by charged particles alters surface chemical composition. Each process leaves distinct spectral signatures. We present a novel data-driven analysis of JWST NIRSpec-IFU observations of Europa's leading hemisphere across three observing geometries, targeting nine spectral bands sensitive to water ice, radiolytic products, and volatiles. Through spectral factorization, we isolate the dominant components of spectral variability and reconstruct their spatial distributions. We find that CO2 enrichment extends beyond Tara Regio, and covers multiple chaos units in a lens-like pattern. These CO2-enriched areas co-occur with anomalous ice-texture signatures. Together, these findings suggest that enrichment in volatiles on Europa may reflect retention-favorable near-surface microphysics as well as emplacement, refining how they are interpreted in the context of surface--interior exchange. This has implications for interpreting the sources and supply rates of extant carbon-bearing species and, ultimately, for assessing Europa's habitability.

Figures (12)

• Figure 1: Selected spectral bands in Europa's normalized NIRSpec-IFU reflectance spectrum. Top: Europa's normalized disk-integrated reflectance spectrum, with seven color-coded spectral bands corresponding to key absorption features. The molecular bands are labeled a--h, and the newly characterized broadband absorption features are labeled with the Greek letters $\zeta$ and $\eta$. Bands marked with an asterisk (a, c, f, g, and h) have been rectified to remove the continuum before further analysis (see Appendix \ref{['sec: obs and reduction']}). The positive, narrow, spike-like features are a residual signal due to differences between the Sun and the calibration star.
• Figure 2: Spectral and spatial modes of Europa's diagnostic bands. Left: zeroth and first spectral modes, $v^{(0)}$ (gray) and $v^{(1)}$ (black) (see Section \ref{['sec: principal spectra']}). The left and right ordinates give the true extrema of $v^{(0)}$ and $v^{(1)}$, marked by gray and black squares in panel (a), while the plotted curves are rescaled for clarity. Middle: spectra from the spaxels where the first spatial mode ($u^{(1)}$) peaks (blue) and reaches its minimum (red), each scaled so its own maximum is 1 (minima shown relative to that peak). The left ordinate corresponds to the blue spectrum and the right ordinate to the red spectrum, as indicated by the colored squares in panel (a); both spectra are rescaled for presentation. Right: first spatial mode, $u^{(1)}$, corresponding to the principal spectra shown in the middle and left panels (see Section \ref{['sec: spatial modes']}).
• Figure 3: Qualitative projections of best-fit spherical harmonic models for the first-order spatial modes, $u^{(1)}$, associated with four molecular bands (labeled a-h, excluding the H$_2$O$_2$ feature) and two newly characterized broadband continuum band-widening features (labeled $\zeta$,$\eta$), overplotted on a binary mask of Tara (black; right-hand feature) and Powys (black; left-hand feature) Regiones. Colors indicate the signed values of $u^{(1)}$ (blue: positive; red: negative), scaled to the extrema of each fitted mode; corresponding numerical ranges are shown in Figure \ref{['fig: spectrum_decomposition']}.
• Figure 4: Significance matrices of Pearson correlations between best-fit spherical-harmonic coefficients of the first-order spatial modes across spectral bands and rescaled and orthographically-projected terrain masks leading hemisphere with a binary mask of Tara and Powys Regiones (see the Appendices). Lower-triangular panels report pairwise Pearson correlation coefficients (text) between bands; color encodes statistical significance after false discovery rate correction benjamini1995controlling. The color bar shows the corresponding Z-score derived from FDR-adjusted $p$-values; greener indicates higher significance. Note: Correlation values displayed here are accurate up to a sign, consistent with the inherent sign indeterminacy of SVD golub2013matrix.
• Figure 5: Qualitative projections of the best-fit three-dimensional spherical-harmonic model to the jointly decomposed first spatial mode, $u^{(1)}$, derived from three viewing geometries of Europa's leading hemisphere. (e) Water-ice 3.1 µm Fresnel peak ($\ell_{\rm{max}}=6$). (g) CO$_2$ absorption doublet near 4.25 µm ($\ell_{\rm{max}}=7$). Shaded outlines mark Tara, Powys, and the leading-hemisphere part of Annwn Regiones. The left panels show jointly decomposed spectral modes ($v^{(0)}$ and $v^{(1)}$ in gray and black, respectively) and spectra from the spaxels where the joint spatial mode peaks (blue) and reaches its minimum (red).