Extraterrestrial liquid water to have water, including liquid pressurised by non-atmospheric means, dissolved into mineral through ionising radiation. Water has also been found to flow on the large asteroid 4 Vesta heated through periodic impacts. Most known extrasolar planetary systems appear to have very different compositions to the Solar System, though there is probably sample bias arising from the detection methods. The goal of current searches is to find Earth-sized planets in the habitable zone of their planetary systems (also sometimes called the "Goldilocks zone"). Planets with oceans could include Earth-sized moons of giant planets, though it remains speculative whether such 'moons' really
Extraterrestrial liquid water ice' or 'superfluid water'. Models of heat retention and heating via radioactive decay in smaller icy Solar System bodies suggest that Rhea, Titania, Oberon, Triton, Pluto, Eris, Sedna, and Orcus may have oceans underneath solid icy crusts approximately 100 km thick. Of particular interest in these cases is the fact that the models indicate that the liquid layers are in direct contact with the rocky core, which allows efficient mixing of minerals and salts into the water. This is in contrast with the oceans that may be inside larger icy satellites like Ganymede, Callisto, or Titan, where layers of high-pressure