Extraterrestrial liquid water not. Similar indirect evidence, however, supports the existence of liquids below the surface of several moons and dwarf planets elsewhere in the Solar System. Some are speculated to be large extraterrestrial "oceans". Liquid water is thought to be common in other planetary systems, despite the lack of conclusive evidence, and there is a growing list of extrasolar candidates for liquid water. As of December 2015, the confirmed liquid water in the Solar System outside Earth is 25-50 times the volume of Earth's water (1.3 billion cubic kilometers). Water on Mars exists today almost exclusively as ice, with a small amount
Phase (matter) liquid water. Increasing the pressure drives the water into the higher density phase, which causes melting. Another interesting though not unusual feature of the phase diagram is the point where the solid–liquid phase line meets the liquid–gas phase line. The intersection is referred to as the triple point. At the triple point, all three phases can coexist. Experimentally, the phase lines are relatively easy to map due to the interdependence of temperature and pressure that develops when multiple phases forms. See Gibbs' phase rule. Consider a test apparatus consisting of a closed and well insulated cylinder equipped with a piston.