Modeling Magnesium Carbonate Precipitation in Jezero Crater

Ancient lakes on Mars, like Jezero Crater paleolake, are candidate locations to look for ancient life because they may have had the right parameters for life to originate. Cyanide and phosphate, which are essential for prebiotic synthesis, can accumulate to high quantities from cyclic evaporation and refilling of carbonate-rich lakes during Mars past, and carbonate signatures in Jezero have been detected from orbit. A key step in the origin of life, as we know it, is the ability for RNA to self-replicate, which requires concentrations of magnesium between 30-50 mM for catalysis (e.g., work by Szostak et al.). In order to determine if magnesium concentrates enough before it precipitates as a carbonate, we use PHREEQC to model the concentration of magnesium in a hypothetical Martian brine and the phases that precipitate out of solution during evaporation at Martian temperatures and pressures. We create a hypothetical Martian brine using a terrestrial analog of groundwater composition from ultramafic rocks but altering composition based on Martian parameters. We also use experimental methods to check the model, as some magnesium carbonates like magnesite and hydromagnesite only form in specific conditions such as the presence of high temperatures and the presence of microbes, respectively. We evaporate a Martian brine simulant in the lab and analyze the residual solids using x-ray diffraction to observe signatures of known crystalline forms of magnesium carbonate.