Enceladus : perhaps one of the several moons to host life in the solar system?

Discovered on August 28th, 1979 by William Herschel, Enceladus is the 6th largest moon of Saturn, but relatively small as it's just 10% the size of Titan, the largest. 500 kilometres in diameter, it is mostly covered by ice therefore being quite reflective. Due to the high amount of sunlight it reflects, it's surface temperature is a frigid -201°C.

Enceladus as viewed in Celestia

In 2005, the Cassini probe performed several flybys of the moon, revealing more information about it's surface and environment than previously known. To elaborate, the probe discovered water plumes emerging from the south polar region as well as cryovolcanoes (volcanoes that emit ice, water, etc.) emitting jets of water, methane and ammonia at roughly 220 kg/s. A percentage of the released material falls back down towards the surface while the rest escapes, contributing to the composition of Saturn's rings. In 2014, NASA reported indications of a subsurface ocean with liquid water about 10 km in depth.

Plumes of water emerging from Enceladus' south pole

Subsurface oceans

Several other natural satellites of the 2 large gas giants Jupiter and Saturn are thought to contain subsurface oceans. Namely, these are Titan, Europa, Enceladus while Callisto, Ganymede and Triton are less likely candidates. 

Data from the Cassini probe in 2005 indicated the existence of liquid water on Enceladus. As aforementioned, astronomers and scientists alike noticed plumes of water in it's south polar region emitting 250 kg of water every second.

Artist's rendition of the interior of the moon, showing a global liquid water ocean between it's crust and core 

The heavier particles in the plumes, which consist of sodium chloride, fall back down to it's surface whereas the lighter particles escape the moon, contributing to the makeup of Saturn's E ring. Thus the presence of salt indicates that the possibility of a salty subsurface ocean, akin to those on earth, but almost 3 times as deep.

The top part of the global ocean, near the north pole, is thought to be located 30-40 km beneath the ice crust and is probably about 10 km in depth. Further evidence of the ocean includes libration of the moon as it orbits Saturn (oscillation of Enceladus relative to Saturn) suggests that the ice crust and rocky core are not in contact with each other and therefore a global ocean exists between the two layers.

For life to exist there, liquid water along with other gases just as carbon and hydrogen as well as some sort of heating must exist. Regarding the latter, there are several ways through which the moon could retain heat, one of which is tidal heating.

Tidal heating

Also referred to as tidal flexing, this process occurs through tidal acceleration (the effect of tidal forces between 2 bodies, in this case Saturn and Enceladus) : orbital as well as rotational energy are dissipated as heat in it's oceans or surface.

It is therefore quite possible for life to exist not only on Enceladus but on several other moons, the only way to confirm this would be through rovers or perhaps even manned exploration, though the latter may be a bit ambitious as of now.