Reflectance spectra of hydrated chlorine salts: The effect of temperature with implications for Europa

by Hanley, J.; Dalton, J. B.; Chevrier, V. F.; Jamieson, C. S.; Barrows, R. S.

Hydrated chlorine salts are expected to exist on a variety of planetary bodies, including inner planets such as Mars and outer planet satellites such as Europa. However, detection by remote sensing has been limited due to a lack of comparison data in spectral libraries. In addition, at low temperatures spectral features of many H2O-bearing species deviate from their room temperature behavior. Thus, we acquired spectra of NaCl, NaClO(4)nH(2)O, MgCl(2)nH(2)O, Mg(ClO4)(2)6H(2)O, and Mg(ClO3)(2)6H(2)O from 0.35 to 2.5 mu m at both 298 and 80K to observe the effects of temperature on diagnostic spectral features. In the near-infrared, the strongest spectral features often arise from water molecules. Increasing hydration states increases the depth and width of water bands. Interestingly, at low temperature these bands become narrower with sharper, better defined minima, allowing individual bands to be more easily resolved. We also measured frozen eutectic solutions of NaCl, MgCl2, and KCl. We show that while care must be taken to acquire laboratory spectra of all hydrated phases at the relevant conditions (e.g., temperature and pressure) for the planetary body being studied, chlorine salts do possess distinct spectral features that should allow for their detection by remote sensing.

Journal of Geophysical Research-Planets
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2169-9100; 2169-9097