5:15 PM - 6:45 PM
[MIS19-P03] Investigations for metals in basalt-hosted hydrothermal environments: Implications for habitability of Europa
Keywords:Hydrothermal activity, Trace metals, Europa, Laboratory experiments
Seafloor hydrothermal activity is one of essential factors for the emergence of life and habitability of extraterrestrial life. It can work as a source of various compounds necessary for life, including metals. Specific metals (e.g., Co and Ni) are used as enzyme cofactors of primitive microbes, such as methanogenic life. Bioavailability of these metals provides direct impacts on the activity of terrestrial methanogens (e.g., Choong et al., 2016).
Here, we conducted a laboratory experiment to investigate the behaviors of multiple metals (Fe, Co, Ni, Cu, Mo) in basalt-hosted hydrothermal activity. Basalt-hosted hydrothermal environments are not only present in the ocean of Earth but also suggested in extraterrestrial ocean worlds, including Jupiter's satellite Europa (Tan et al., 2021). As starting rock, we used an eucrite, one of the typical basaltic meteorites. Microscopic analyses shows that metals are mainly contained in Fe sulfides in the starting rock. A starting solution contained 1 mol/L of NaCl and 0.01 mol/L of H2SO4. We measured concentrations of dissolved species in a gold reaction cell during ~3000 hours of reactions between rock and solutions at 300 °C and 50 MPa.
Our experimental results show that Fe and Ni concentrations reach ~100 and ~10 μmol/L, respectively. Concentrations of Co, Cu, and Mo are ~1 μmol/L. These metal concentrations are comparable to their optimal values for terrestrial methanogens (e.g., Choong et al., 2016). The in-situ pHs of the solution are calculated as around 6 during the experiment, which are nearly neutral pH values at the condition.
Based on our microscopic analyses, the metals would be contained as metallic sulfides (e.g., CoS). Our thermodynamic equilibrium calculations also suggest that the solubilities of metallic sulfides can reproduce dissolved concentrations of these metals. In addition, metal dissolutions are promoted by formations of dissolved complex species, such as chloride complexes (e.g., CoCl+, CoCl2,aq). High Cl concentrations stabilize chloride complexes under acidic-to-neutral hydrothermal conditions. Cl concentrations of Europa's seawater are estimated in wide ranges up to ~0.1-1 mol/L (e.g., Melwani-Daswani et al., 2021). If the seawater is rich in Cl, H2 production in water-rock reactions would be maintained throughout Europa's history (Speirs & Schmidt, 2023). Our results suggest that such Cl-rich seawater could be effective for life in terms of the availability of metals as well.
Here, we conducted a laboratory experiment to investigate the behaviors of multiple metals (Fe, Co, Ni, Cu, Mo) in basalt-hosted hydrothermal activity. Basalt-hosted hydrothermal environments are not only present in the ocean of Earth but also suggested in extraterrestrial ocean worlds, including Jupiter's satellite Europa (Tan et al., 2021). As starting rock, we used an eucrite, one of the typical basaltic meteorites. Microscopic analyses shows that metals are mainly contained in Fe sulfides in the starting rock. A starting solution contained 1 mol/L of NaCl and 0.01 mol/L of H2SO4. We measured concentrations of dissolved species in a gold reaction cell during ~3000 hours of reactions between rock and solutions at 300 °C and 50 MPa.
Our experimental results show that Fe and Ni concentrations reach ~100 and ~10 μmol/L, respectively. Concentrations of Co, Cu, and Mo are ~1 μmol/L. These metal concentrations are comparable to their optimal values for terrestrial methanogens (e.g., Choong et al., 2016). The in-situ pHs of the solution are calculated as around 6 during the experiment, which are nearly neutral pH values at the condition.
Based on our microscopic analyses, the metals would be contained as metallic sulfides (e.g., CoS). Our thermodynamic equilibrium calculations also suggest that the solubilities of metallic sulfides can reproduce dissolved concentrations of these metals. In addition, metal dissolutions are promoted by formations of dissolved complex species, such as chloride complexes (e.g., CoCl+, CoCl2,aq). High Cl concentrations stabilize chloride complexes under acidic-to-neutral hydrothermal conditions. Cl concentrations of Europa's seawater are estimated in wide ranges up to ~0.1-1 mol/L (e.g., Melwani-Daswani et al., 2021). If the seawater is rich in Cl, H2 production in water-rock reactions would be maintained throughout Europa's history (Speirs & Schmidt, 2023). Our results suggest that such Cl-rich seawater could be effective for life in terms of the availability of metals as well.