Ocean Worlds Exploration Program

Prime targets include moons that harbor hidden oceans beneath a shell of ice: Europa, Enceladus, and Titan.

A host of other bodies in the outer Solar System are inferred by a single type of observation or by theoretical modeling to have subsurface oceans.

"[15] The report noted that development of OWEP-enabling technologies must currently compete for priority with other Solar System objectives, which is not useful for strategic planning.

[3] The planning also considers implementing planetary protection measures to avoid contaminating extraterrestrial habitable environments with resilient stowaway bacteria on their landers.

[3][4] Ocean worlds identified in the Solar System so far with reasonable certainty are the major moons Europa, Enceladus, Titan, Ganymede, and Callisto.

Bodies such as Triton, Pluto, Ceres, Miranda, Ariel, and Dione are considered candidate ocean worlds, based on hints from limited spacecraft observations.

Two possible models of Europa
Artist's impression of possible hydrothermal activity on Enceladus's ocean floor [ 10 ]
Artist's cut-away representation of the internal structure of Ganymede. Layers drawn to scale.