Flexi Says: For a planet to have a water cycle, water must exist in different reservoirs on the planet's surface and have some way to move between them. On Earth, this often involves a change in state. Several planets and moons in our solar system are known to have water, though in several cases the water seems to be trapped in a single state and therefore does not cycle. For example, Mars most likely has frozen water beneath the ground surface. However, this water does not move through the atmosphere or form liquid bodies of water on the surface. One of Saturn's moons, Enceladus, is known to have water in all three states and scientists have observed some processes that move the water from one state to another. Therefore, it is reasonable to conclude that Enceladus has some type of water cycle, though the details may be very different than Earth's water cycle. Scientists are also interested in studying exoplanets that have water, though the technology to do so is very early in development.