There are four large moons located close to the planet , which were first discovered by Galileo. The densest and closest of these large moons is , which also has a warm melted interior, kept warm by a process known as This moon shows a lot of active as a result. The second of these four large moons (in a row) is also heated by this process and there is evidence that under its crust of ice, there is This second large moon is called The third of these large moons happens to be the largest moon in our solar system, and is called . Some of its surface looks quite old, while other parts show evidence of being significantly younger. The planet with the most significant ring system has just one large moon, called This moon has a thick with pressures at the surface greater than on Earth or Mars. At the surface, this moon has rivers and lakes made of and other hydrocarbons..