Abundant Phosphorus in Enceladus’ Ocean

Illustration of the layers of Enceladus depicting the rocky core to weather, releasing dissolved phosphorus into the ocean. Credit: Southwest Research Institute.

The search for life on other worlds has focused on liquid water. However, water is not the only necessary ingredient for a habitable environment. Enceladus, one of the moons of Saturn, is an ocean world with plumes erupting from cracks in its icy surface. These plumes of ice grains and water vapor were analyzed by a NASA spacecraft called Cassini, whose mission was to study Saturn and its moons. When Cassini flew through the plumes, it detected almost all the basic requirements for life as we know it. Yet, one of the elements essential for life, phosphorus, was not detected in the plumes. Phosphate molecules, which consist of phosphorus and oxygen atoms, are key to life as we know it on Earth. The formation of DNA and RNA, cell membranes, and energy-carrying molecules all require phosphates.

Previous models have suggested that phosphorus might be scarce in the subsurface ocean of Enceladus, implying that prospects for life there are dim. However, recent work by Jihua Hao from the University of Science and Technology of China and colleagues suggests that the ocean should be relatively rich in phosphorus. Based on knowledge about the ocean-seafloor system from Cassini and previous models, they performed thermodynamic and kinetic modeling that simulated the geochemical processing of phosphorus. The model assumed that there was a permeable and porous layer directly below the seafloor, where exchange between the ocean water and rock could occur. The model focused on how various minerals dissolved and interacted with the ocean. The results suggest that the phosphate minerals are unusually soluble and that phosphorus levels in the ocean might be higher than previously thought, perhaps approaching or surpassing those in Earth’s seawater. These new estimates of the phosphorus content in Enceladus’ subsurface ocean greatly increase the chances that life there is possible. READ MORE