Low temperature characterization of hydrohalite and related salts essential to life in the Atacama

Grant #: NNX13AI67G
Senior Scientist: Janice Bishop

We propose to extend an existing project funded by the Astrobiology: Exobiology and Evolutionary Biology program to study cyanobacteria inside Atacama halite pinnacles that will enable characterization of these potential habitats on other planetary bodies. Hygroscopic salts are the best-known habitat for life in extremely water-deprived environments, and their identification in other planetary bodies would make them a key target for the search for life. We have designed experiments to measure Visible/near-infrared reflectance spectroscopy of a variety of samples from this current project in a low temperature chamber. Halite pinnacle samples from that study as well as synthetic hydrohalite and related hygroscopic Cl salts grown under low temperatures will be characterized at -190 to +10 °C in our proposed project. Hydrohalite is a hydrated NaCl mineral below 0 °C, but is unstable above 0 °C and converts to halite (NaCl) at room temperature. Hydrohalite (NaCl•2H2O), magnesium chloride dodecahydrate (MgCl2•12H2O) and iron chloride hexahydrate (FeCl2•6H2O) are all unstable above 0 °C on Earth, but are expected to be the dominant phase of salts in the cold environments of Mars and other bodies in the Solar System. Antarcticite (CaCl2•6H2O) is observed below 0 °C in the Antarctic, as well as up to 30 °C in the Mojave Desert. We propose to characterize the stability and spectral properties of these hydrated salts and Atacama halite samples under low temperature and reduced pressure conditions. These experiments will identify the spectral fingerprints of hydrated Cl salts over a range of temperatures and enable determination of their viability on planetary surfaces (e.g. Mars, Enceladus). 

Understanding the spectral properties of these unique mineral habitats will enable detection of these on Mars and other bodies. Halite has been found at the Phoenix landing site on Mars and tentative identifications of halite have been made using CRISM spectral data from orbit. Our experiments will provide essential data for identification and characterization of hydrohalite and other hydrated Cl salts on Mars. Low-temperature NaCl salts appear to be present on Enceladus as well. Characterizing the spectral properties of hydrated Cl salts will thus enable remote sensing searches for these minerals that could support favorable habitats in our Solar System.