¹Jennifer Hanley,²J. Brad Dalton III,³Vincent F. Chevrier,⁴Corey Jamieson,⁵R. Scott Barrows
¹Southwest Research Institute, Department of Space Studies, Boulder, CO, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
³Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR, USA
⁴SETI Institute, Mountain View, CA, USA
⁵Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO, USA

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, NaClO4∙nH2O, MgCl2∙nH2O, Mg(ClO4)2°6H2O, and Mg(ClO3)2°6H2O from 0.35-2.5 µm at both 298 and 80 K to observe the effects of temperature on diagnostic spectral features. In the NIR, 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, pressure) for the planetary body being studied, chlorine salts do possess distinct spectral features that should allow for their detection by remote sensing.

Reference
Hanley J, Brad Dalton III J, Chevrier VF, Jamieson C, Barrows RS (2014) Reflectance Spectra of Hydrated Chlorine Salts: The Effect of Temperature with Implications for Europa. Journal of Geophysical Research (in Press)
Link to Article [DOI: 10.1002/2013JE004565]

Published by arrangement with John Wiley & Sons