  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.
