¾Ã¾ÃÈÈ

Mentor(s): James Leong, Ph.D., Marion Lytle, Ph.D., and Dongyi Guo

Phosphorus is a critical bioessential element, yet its availability in extraterrestrial ocean worlds remains largely unknown. Bioavailable phosphorus is derived from the weathering of phosphate-bearing minerals like hydroxyapatite. In this study, we investigated the dissolution of hydroxyapatite in four solutions—0.1 M hydrochloric (acidic pH), deionized water (neutral to slightly acidic pH), 0.1 M sodium bicarbonate (alkaline pH), and 0.1 M sodium carbonate (very alkaline pH) —to assess the potential for phosphorus mobilization at various pH conditions. The carbonate-rich and alkaline solutions are analogous to Saturn’s moon Enceladus. Our results indicate that sodium bicarbonate and sodium carbonate solutions effectively mobilize more phosphate (2x and 2-3x, respectively) relative to neutral pH conditions. The carbonate-rich and alkaline conditions enhance hydroxyapatite dissolution and facilitate phosphorus accumulation by reducing the availability of divalent Ca ions via calcite precipitation. These experimental findings align with recent geochemical models of Enceladus’s ocean, which predict high P concentrations at alkaline conditions (Hao et al., 2022). Given that Enceladus’s ocean should be relatively rich in dissolved phosphorus, our experimental results further support the potential habitability of such environments. This work contributes to the broader understanding of how phosphorus cycling in ocean worlds may influence prebiotic chemistry and the prospects for life beyond Earth.