Contribution of Non‐Water Ices to Salinity and Electrical Conductivity in Ocean Worlds

Modeling of the electrical conductivity (EC) of icy moon oceans has previously assumed that chloride, sulfate, and other ions released from rock leaching are the main solutes and carriers of EC. Here, we show that accreted volatiles, such as carbon dioxide and ammonia, can add a significant fraction of solutes in bodies whose volatile content was in part supplied from cometary materials. These volatiles can increase the EC of aqueous solutions above 1 S/m. Our salinity and EC estimates can serve as a basis for planning future magnetometer investigations at icy moons and dwarf planets. In particular, oceans expected in some of the Uranian satellites and Neptune's satellite Triton could have EC above 3 S/m as a result of accretion of both carbon dioxide and ammonia, even if rock leaching during water‐rock separation was limited, and if chlorine and sulfur abundances may be at CI carbonaceous chondritic levels. Plain Language Summary Searching for deep oceans in icy bodies is a major driver of planetary exploration. Magnetometry is used to detect electric currents in deep oceans generated by a varying magnetic field, from a giant planet or solar wind, as was done at Jupiter's moon Europa during the Galileo mission. Previous studies have assumed that the salinity of deep oceans is determined by the leaching of major elements from accreted rock, which may yield brackish and low electrical conductivity solutions. We show that carbon dioxide, an abundant ice in the outer solar system, could contribute a significant fraction of solutes (carbonate and bicarbonate ions) in ocean worlds, regulated in particular by the presence of ammonia. The latest solar system dynamical models predict that dwarf planets and most icy moons accreted ices rich in carbon dioxide and ammonia. If oceans exist today inside these bodies, the resulting ion concentrations would produce a stronger magnetic signature than previously expected, perhaps detectable by future spacecraft missions. Key Points Accreted CO2 and NH3 ices can significantly increase the salinity and electrical conductivity (EC) of deep oceans Water to rock ratio and ammonia abundance drive the concentrations of carbonate and bicarbonate ions in solution Predicted EC estimates can be used to plan future ocean search missions at icy moons and dwarf planets