Ocean planets

Ocean planets, often called water worlds, contain vast amounts of water—far more than Earth, where oceans make up only a tiny fraction of the planet's total mass. Water can cover the entire surface tens of kilometers deep or hide beneath a thick icy crust, similar to Jupiter's moon Europa in our solar system. Whether water remains liquid depends on the distance from its star and atmospheric conditions. These worlds have a lower density than purely rocky planets. Under the extreme pressure of deep global oceans, exotic forms of high-pressure ice often freeze at the bottom, separating the water layer from the rocky core.