Applicant — Katie Primm

Stable brine forms when the temperature, relative humidity, and salt-mass percentage are within stable bounds that are dependent on the salt type. Mars is dry and temperature and relative humidity are anti-correlated, making the presence of surface brine challenging. Throughout my graduate and postdoctoral careers I used two experimental apparatuses and analytical techniques to study the different ways that liquid brines could be present on the surface and subsurface of Mars. For my graduate research, I used a Raman microscope outfitted with an environmental cell to study individual micron sized particles (e.g. perchlorate and chloride salts) as they underwent temperature and humidity changes. I investigated the changes in the particle structure visually through the microscope and spectrally using Raman spectroscopy and determined that the extent of metastability of brines was much larger as the particles froze at colder temperatures than previously predicted. Using these techniques, I was also able to provide a more complete thermodynamic phase diagram of MgCl₂. Throughout my postdoc, I built a remotely controlled experimental Mars chamber to simulate Martian conditions at varying temperatures, humidities, and pressures. Here, the samples were bulk in size (rather than micron sized particles as before) and dielectric spectroscopy was used to study the water uptake and release of the samples (e.g. perchlorate salts mixed with regolith analogs). Through preliminary studies, I found that at warm temperatures, brines start to form quickly, but take almost 12 hours to fully saturate the pores. This could mean that if brines are present, they would exist in very small volumes. In addition to experimental studies, I have worked with researchers to develop models for the salt and atmospheric interaction using orbital and rover data. Results of these models indicate that the subsurface of Mars is a better host for brines and that there is a strong possibility of brines being present at the Phoenix landing site rather than Gale Crater.