Looking for Oceans in the Solar System: Updates and Future Perspectives

The outer Solar System hosts a wide variety of regular moons that contain a significant fraction of water. Whether this water could be stable in the liquid phase on a planetary scale to form a global ocean is a question that has driven substantial research in the last few decades, motivated by the potential for habitability connected to the combination of liquid water, energy and nutrients that a global ocean might offer. The Galileo and Cassini missions acquired measurements that confirmed the existence of subsurface oceans at several moons of Jupiter and Saturn, while numerical modeling predicts the potential preservation of oceans beneath the surfaces of Uranus’s moons. The next decades will offer exciting opportunities to test for the presence of oceans in the outer Solar System with the data that will be acquired by Europa Clipper and Juice in the Jupiter system, Dragonfly at Titan, and the anticipated Uranus Orbiter and Probe in the Uranus system. I will review the techniques that have been used or proposed to establish the presence of oceans in icy moons based on spacecraft measurements. I will present recent work that challenges the long-standing interpretation that Titan hosts a subsurface ocean based on improved measurements of its gravity field and a reassessment of other observations, which are best explained by an interior model without a global ocean. This result also has implications for detecting oceans inside Callisto and Ganymede, where confirmation will likely require combining observations from multiple investigations of Europa Clipper and Juice. Finally, I will show recent work on the formulation efforts of the Uranus Orbiter and Probe mission at JPL, with a focus on a preliminary strategy to reveal oceans inside Uranus’s major moons by optimizing the observation plan under the stringent design, operational constraints, and limited resources of such a challenging mission.