Fig. 2. Total dissolved phosphate concentration (mol/kg) for averaged carbonaceous chondrite composition for different chondrite classes and mid-ocean ridge basalts with 0–2 wt% C.

a–c CI, CM, CR are closer to solar stoichiometry and d–f CV, CO, CK have higher Ca concentrations. For comparison with Europa, vertical lines are inferred from hydrothermal models³⁵ and the horizontal line is the lower bound on water/rock ratio inferred from salinity estimates¹³. For comparison with Enceladus, shaded regions show estimates from Si nanoparticles¹¹ while horizontal lines track modeled [Na] corresponding to observations of NaCl observed in the E-ring¹⁰ (additional pH constraints Fig. 3).