Where else can liquid water be found elsewhere in the galaxy? The first constraint is related to the conditions of temperature and pressure.
Planets of the Solar System and water
The Solar System gives us valuable information about the possibilities of existence of liquid water.
The eight planets of the Solar System are very clearly divided into two categories: the four planets closest to the Sun are small and rocky ("telluric planets"), the four most distant planets are enormous and mainly constituted of gas ("gas giants "). But this distinction is associated with another fundamental difference: most gaseous giant satellites are mostly water ice, while terrestrial planets are rather poor in water (including the Earth, where the oceans are deep only 2 kilometers while the rocky body is 6,380 km radius ...). These two findings are interrelated:
far from the Sun, the water is present in the form of ice. As it is a very abundant molecule, it has been added significantly to the mass of rock bodies during the formation of the Solar System. Thanks to the weakness of solar radiation, these large rock nuclei have retained the lightest gases such as helium and dihydrogen: since these two gases are by far the most abundant in the universe, these planets have grown inordinately up to to become gaseous giants, surrounded by a procession of frozen satellites;
near the Sun, the intensity of radiation has tended to break any molecule of water in the space vacuum, and water has not been added to the mass of rock bodies. In addition, these radiations prevented light gases such as helium and dihydrogen from accumulating on the surface: the planets could only retain a fine atmosphere above water-poor rock bodies.