Organic Preservation Pathway for UV and Perchlorate-Rich Parts of Mars: Oxidative Polymerization of Organic Compounds on Iron(III)-Rich Goethite

Perchlorate salts are widespread on Mars and are commonly regarded as a potential barrier to organic preservation because ultraviolet (UV) irradiation may activate perchlorate photochemistry and generate destructive oxychlorine species. Despite this, multiple rover missions have identified indigenous organic compounds in Martian sediments, indicating that preservation pathways remain incompletely understood. Previous work showed that Fe(III)-rich minerals such as goethite can promote oxidative coupling of aromatic organic compounds under Mars-analog conditions, producing higher molecular weight products that should be more resistant to degradation. Here, we examine whether UV-irradiated perchlorate suppresses mineral-mediated oxidative polymerization of 2-naphthol adsorbed onto goethite under those same conditions. Across organic loadings of 0.5 to 10 wt %, oxidative coupling proceeded in the presence of magnesium perchlorate, yielding dimers and higher-order oligomers. Yields were not measurably suppressed on experimentally relevant hour time scales. Our results provide experimental constraints on the competition between perchlorate photochemistry and mineral surface oxidative coupling under dry, Mars-analog UV conditions. This may represent a potential preservation mechanism in perchlorate-bearing, iron-rich Martian sediments.