Shedding\nLight on the Kinetics of the Carboxysulfitic\nScenario

One way in which we can attempt to relate chemical pathways\nto\ngeochemical environments is by studying the kinetics of a given sequence\nof reactions and identifying the conditions under which this chemistry\nis the most productive. Many prebiotic reactions rely on a source\nof fixed carbon; therefore, chemical pathways that suggest prebiotically\nplausible ways of fixing carbon are of significant interest. One such\npathway is the carboxysulfitic reaction network, which uses solvated\nelectrons, produced as a result of electron photodetachment from sulfite,\nto reduce carbon. In this work, we explore carboxysulfitic chemistry\nat three different pH values: 6, 9, and 12. We utilize a new light\nsource, that matches the broadband spectral shape of the young Sun,\nto irradiate a mixture of bicarbonate and sulfite. We determine the\nrate equation for the production of formate from these compounds and\nfind the order to be 0.71 ± 0.12 with respect to bicarbonate\nand −0.60 ± 0.10 with respect to sulfite. Following this,\nwe determine rate constants for the production of formate considering\ntwo different mechanisms. We find this chemistry to be feasible at\nall three of the pH values tested, with the magnitude of the rate\nconstants being highly dependent on the assumed mechanism. We suggest\nthat these results may have implications for Mars Sample Return owing\nto Jezero Crater having had lakes similar to those in which we propose\ncarboxysulfitic chemistry to have been the most productive. Due to\nMars’ relatively unaltered surface, we propose that Mars Sample\nReturn missions could look for preserved tracers of this chemistry,\nshedding light on Mars’ past conditions and its potential for\nhaving hosted life.