FOLLOWING THE WATER ON MARS: A MOLECULAR LEVEL STUDY FOR LIQUID SALTY BRINE FORMATION IN MARS ANALOGS IN THE MID-IR REGION

H₂O is a simple molecule, yet essential for all living organisms to sustain life. NASA and ESA have focused on the ‘follow the water’ strategy to search for lifeand habitabilityon Mars and other planetary bodies, which is a component of the NASA Perseverance and upcoming ESA Rosalind Franklin Mars rover missions.

The extreme conditions on Mars today allow no stable water on the surface, but various types of chloride and perchlorate salts that have been widely detected in martian regoliths across equatorial and mid-latitude regions could facilitate the formation of liquid salty brines well below 0 °C due to the deliquescence properties of these salts. Such liquid salty brines can also be formed and stabilized within aggregates of mineral particles by forming thin water films.

While previous studies with Cl-bearing salts mainly focused on their deliquescence/efflorescence features, some of our recent studies specifically focused on the effect of Mars analogs on the low temperature phase changes of briny water. In our experiments, we aim to identify the complex relationships of Cl salts in Mars analogs as they transform from the permafrost state to a liquid salty brine and then to thin water films formed in soil aggregates using cryogenic FTIR spectroscopy in the mid-IR region. In this study, we used two volcanic soils from Hawaii plus the Mojave Mars Simulant (MMS) with varied particle size distributions and chemical compositions. We mixed these samples with 40% wt. CaCl₂and 10% wt. Mg(ClO₄)₂solutions. These mixtures were flash-frozen at -90 °C as a coating on a precooled temperature controlled Attenuated Total Reflectance (ATR) stage. The temperature was slowly increased up to 25 °C while continually collecting spectra in order to monitor the phase changes of the frozen/liquid salty brines. We observed that each sample has distinct spectral features at -90 °C depending on the type of Cl salt. As the samples were warmed up, one of the volcanic ash samples presented spectral changes following the phase diagrams of Cl salts including the transition from frozen to liquid salty water, yet the other samples presented liquid salty brine features at higher temperatures than expected. Future studies with cryogenic-XRD are needed to resolve the potential role of salty martian analogs in liquid salty brine formation.