Spatially Resolved Spectroscopy of Europa: The Distinct Spectrum of Large-scale Chaos

TL;DR

This study uses adaptive optics spectroscopy to analyze Europa's surface, identifying three distinct compositional regions and suggesting the presence of endogenous materials like chloride evaporites, challenging previous sulfate-based models.

Contribution

It provides the first spatially resolved spectral analysis of Europa's surface, revealing new insights into its endogenous composition and geological features.

Findings

Three distinct compositional end members identified

Endogenous component shows hydrated minerals but not sulfates

Chloride evaporites are a plausible alternative to sulfates

Abstract

We present a comprehensive analysis of spatially resolved moderate spectral resolution near infrared spectra obtained with the adaptive optics system at the Keck Observatory. We identify three compositionally distinct end member regions: the trailing hemisphere bullseye, the leading hemisphere upper latitudes, and a third component associated with leading hemisphere chaos units. We interpret the composition of the three end member regions to be dominated by irradiation products, water ice, and evaporite deposits or salt brines, respectively. The third component is associated with geological features and distinct from the geography of irradiation, suggesting an endogenous identity. Identifying the endogenous composition is of particular interest for revealing the subsurface composition. However, its spectrum is not consistent with linear mixtures of the salt minerals previously considered relevant to Europa. The spectrum of this component is distinguished by distorted hydration features rather than distinct spectral features, indicating hydrated minerals but making unique identification difficult. In particular, it lacks features common to hydrated sulfate minerals, challenging the traditional view of an endogenous salty component dominated by Mg-sulfates. Chloride evaporite deposits are one possible alternative.