The locations of subsurface oceans are on Europa, Enceladus, Ganymede, Titan, the asteroid Ceres, Callisto, Dione and Pluto.
There also could be subsurface oceans at Rhea, Titania, Oberon, Triton, Orcus, MakeMake, Eris, 2007 OR10, and Sedna.
There is also a lot of water ice on Mars.
There was a recent paper in Geophysical Review Letters which provided analysis of NASA Cassini space probe data which provided more evidence of the subsurface oceans on Enceledus and Dione. There have been imaging of water plumes from the Hubble Telescope from Europa.
The Spitzer Space Telescope discovered that Enceladus, a moon of Saturn, has water volcanoes spouting up through cracks in its icy surface. The Cassini spacecraft at Saturn has learned more about the water volcanoes during its flyby passes of Enceladus.
The most conclusive method for detection and confirmation of extraterrestrial liquid water is currently absorption spectroscopy. Liquid water has a distinct spectral signature to other states of water due to the state of its Hydrogen bonds.
NASA estimates that Europa’s subsurface ocean have twice as much water as the whole Earth.
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
At 1122 km (697 mi) in diameter, Dione is the 15th largest moon in the Solar System, and is more massive than all known moons smaller than itself combined. About two thirds of Dione’s mass is water ice, and the remaining is a dense core, probably silicate rock
Callisto is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System and the largest object in the Solar System, Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km
Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. Models suggest that Rhea could be capable of sustaining an internal liquid-water ocean through heating by radioactive decay.
Titania is the largest and most massive Uranian moon, and the eighth most massive moon in the Solar System.Its density of 1.71 g/cm³, which is much higher than the typical density of Saturn’s satellites, indicates that it consists of roughly equal proportions of water ice and dense non-ice components;the latter could be made of rock and carbonaceous material including heavy organic compounds. The presence of water ice is supported by infrared spectroscopic observations made in 2001–2005, which have revealed crystalline water ice on the surface of the moon.
Titania may be differentiated into a rocky core surrounded by an icy mantle. If this is the case, the radius of the core 520 kilometres (320 mi) is about 66% of the radius of the moon, and its mass is around 58% of the moon’s mass—the proportions are dictated by moon’s composition. The pressure in the center of Titania is about 0.58 GPa (5.8 kbar). The current state of the icy mantle is unclear. If the ice contains enough ammonia or other antifreeze, Titania may have a subsurface ocean at the core–mantle boundary. The thickness of this ocean, if it exists, is up to 50 kilometres (31 mi) and its temperature is around 190 K. However the present internal structure of Titania depends heavily on its thermal history, which is poorly known.
Oberon is the second largest and most massive of the Uranian moons after Titania, and the ninth most massive moon in the Solar System. Oberon’s density of 1.63 g/cm³, which is higher than the typical density of Saturn’s satellites, indicates that it consists of roughly equal proportions of water ice and a dense non-ice component.
Oberon may possess a liquid ocean layer at the core–mantle boundary. The thickness of this ocean, if it exists, is up to 40 km and its temperature is around 180 K. However, the internal structure of Oberon depends heavily on its thermal history, which is poorly known at present