Considering chemical evolution toward life on Earth from Enceladus

Saturn's moon Enceladus possesses a Na-carbonate-rich subsurface ocean. According to the in-situ analysis of plume materials erupting from the subsurface ocean, the Cassini spacecraft has revealed that seawater pH is alkaline, near 10, and that hydrothermal activity exists in the rock core. In addition to Na-carbonate-rich plume particles, a new type of phosphate-rich particle was recently discovered. Phosphorus (P) is a CHNOPS element essential for life on Earth, but of these, it is the least abundant in the Earth's aqueous environments. Throughout Earth's history, phosphorus has been the rate-limiting element of biological production. Based on the analysis of phosphate-rich particles of Enceladus, phosphate concentrations in the subsurface ocean would be 1000 times higher than in the Earth's oceans.

To understand the causative mechanism of the enrichment of phosphate in Enceladus' seawater, we performed hydrothermal reaction experiments and geochemical modeling. We find that alkaline (pH ~10) and carbonate-rich aqueous environments are…