Saturn’s moon Enceladus sends signal flares into space that say, “Look here for life!” with every spray of its southern hemisphere geysers. The Cassini mission flew through and sampled the geyser spray in 2015, revealing that beneath Enceladus’s icy crust is a liquid water ocean with high concentrations of dissolved inorganic carbon (DIC), molecular hydrogen (H2), and methane (CH4). These properties make Enceladus a prime candidate for astrobiology missions. But Enceladus’s subsurface ocean i...