The nature of Europaʹs dark non-ice surface material: Spatially-resolved high spectral resolution spectroscopy from the Keck telescope

We present new 1.45–1.75 μm spectra of Europaʹs dark non-ice material with a spectral resolution ( λ / δ λ ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileoʹs near-infrared mapping spectrometer (NIMS) with λ / δ λ = 66 , no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra.