Brine Volume Fraction as a Habitability Metric for Europa's Ice Shell

Brine systems in Europa's ice shell have been hypothesized as potential habitats that could be more accessible than the sub-ice ocean. We model the distribution of sub-millimeter-scale brine pockets in Europa's ice shell. Through examination of three habitability metrics (water activity, ionic strength, and salinity), we determine that brine pockets are likely not geochemically prohibitive to life as we know it for the chloride and sulfate-dominated ocean compositions considered here. Brine volume fraction is introduced as a novel habitability metric to serve as a proxy for nutrient transport and recycling-because of its role in governing permeability-and used to define regions where nutrient-open, nutrient-closed, and relict habitats are stable. Whereas nutrient-closed habitats could exist wherever brine is stable, nutrient-open habitats are confined to meter-scale regions near the ice-ocean interface where freezing is occurring. This classification scheme can help guide future life-detection missions to ocean worlds.

Automated summary

Brine systems in Europa's ice shell may provide potential habitats that are more accessible than the sub-ice ocean. A study shows that these brine pockets are not chemically restrictive to life as we know it in the chloride and sulfate-dominated ocean compositions considered. A new metric called brine volume fraction is introduced to evaluate nutrient transport and recycling, allowing the identification of stable nutrient-open, nutrient-closed, and relict habitats.