SPATIALLY RESOLVED SPECTROSCOPY OF EUROPA’S LARGE-SCALE COMPOSITIONAL UNITS AT 3–4 μm WITH KECK NIRSPEC

Abstract

We present spatially resolved spectroscopic observations of Europa's surface at 3-4 μm obtained with the nearinfrared spectrograph and adaptive optics system on the Keck II telescope. These are the highest quality spatially resolved reflectance spectra of Europa's surface at 3-4 μm. The observations spatially resolve Europa's large-scale compositional units at a resolution of several hundred kilometers. The spectra show distinct features and geographic variations associated with known compositional units; in particular, large-scale leading hemisphere chaos shows a characteristic longward shift in peak reflectance near 3.7 μm compared to icy regions. These observations complement previous spectra of large-scale chaos, and can aid efforts to identify the endogenous nonice species.

The Space Environment of Io and Europa

“…The big question has been whether Europa's alkalis are representative of its brines and ocean salinity (endogenic) or is this merely iogenic material painted onto Europa's surface (exogenic). A recent review by Johnson et al (2019) summarizes the current situation as follows: “Recent ground‐based observations of Europa point towards the presence of endogenic materials (possibly chlorinated salts) on the surface (Brown & Hand, 2013; Fischer et al, 2015, 2016; Ligier et al, 2016), and irradiation experiments by Hand and Carlson (2015) suggest that NaCl‐rich material from the sub‐surface ocean may explain Europa's yellow‐brownish color at visible wavelengths. In addition, the ambient sodium and potassium emissions observed (Brown & Hill, 1996;Brown, 2001) also suggest that there is coupling between the surface and the likely 'salty' ocean (e.g., Johnson, 2000; Leblanc et al, 2002, 2005).…”

The Origin and Fate of O 2 $\mbox{O}_{2}$ in Europa’s Ice: An Atmospheric Perspective

“…That there is coupling has been discussed for years based on the modeling of the images of its nearly craterless and fractured surface (e.g., Pappalardo et al 2009;Parro et al 2016;Kattenhorn and Prockter 2014;Prockter et al 2017). Recent ground-based observations of Europa point towards the presence of endogenic materials (possibly chlorinated salts) on the surface Fischer et al 2015Fischer et al , 2016Ligier et al 2016), and irradiation experiments by Hand and Carlson (2015) suggest that NaCl-rich material from the sub-surface ocean may explain Europa's yellow-brownish color at visible wavelengths. In addition, the ambient sodium and potassium emissions observed (Brown and Hill 1996;Brown 2001) also suggest that there is coupling between the surface and the likely 'salty' ocean (e.g., Johnson 2000;Leblanc et al 2002Leblanc et al , 2005.…”

Natural Analogue Constraints on Europa's Non‐ice Surface Material

“…• Table S1 • Table S2 • Table S3 • Table S4 Correspondence to: M. G. Fox-Powell, mgfp@st-andrews.ac.uk Multiple observations of Europa's non-icy material exist, showing visible near-infrared (vis-NIR) evidence for hydrated compounds (Brown & Hand, 2013;Carlson et al, 2005;Dalton et al, 2012;Fischer et al, 2015Fischer et al, , 2016Ligier et al, 2016;McCord et al, 1999). Such material can form through exogenic and radiolytic processes, salt precipitation from subsurface brines, or a combination of these two mechanisms.…”

“…Previous studies have attempted to explain the shape of europan non-icy spectra with numerical linear mixes of pure salt spectra (Carlson et al, 2005;Dalton, 2007;Ligier et al, 2016) or with experimentally produced salt assemblages (Orlando et al, 2005). Based on these works, hydrated sulfates such as mirabilite (Na 2 SO 4 .10H 2 O) and sulfuric acid hydrate have been proposed as major components of deposits on the trailing hemisphere (Carlson et al, 2005;Dalton et al, 2012;Shirley et al, 2010), whereas chloride salts may contribute to spectral signatures of "chaos" regions (Brown & Hand, 2013;Fischer et al, 2016).…”