Energy yields for acetylenotrophy on Enceladus and Titan

Abstract

Saturn's moons Titan and Enceladus appear to satisfy three key criteria for life: presence of liquid water, nutrient availability, and metabolic energy sources. Consequently, these ocean worlds are the focus of astrobiology research investigations that aim to assess the potential for life beyond Earth. One plausible source of metabolic energy on these moons is acetylene (C2H2), a simple organic compound that is the second most abundant photochemical product in Titan's atmosphere and has been identified as a likely constituent of Enceladus' ocean. Acetylenotrophy, or the microbial fermentation of acetylene, is utilized by microbes on Earth in a number of environments. Here, we have calculated the energy yield of acetylenotrophy to be 69–78 kJ/mol C within the oceans of Titan and Enceladus, greater than the widely considered, hydrogenotrophic methanogenesis, at 25–65 kJ/mol C. Therefore, we propose acetylenotrophy as a potential metabolism on these moons that should be considered in future astrobiology studies on worlds with abundant acetylene.