Photo: AP
The evidence comes from the discovery of seawater salt in ice grains forming Saturn's outermost ring.
Scientists know the "E-ring" is replenished by jets of water and ice spurting hundreds of miles into space from Saturn's sixth largest moon, Enceladus.
The geyser-like plumes erupt from fracture lines known as "tiger stripes" that slice across the moon's south pole.
The new findings suggest the jets originate from a liquid underground source, either a global salty ocean or - more likely - deep cavern reservoirs.
They also indicate that the water, warmed by tidal forces from Saturn's powerful gravity, could be as salty as the Earth's oceans and not too acidic for life. Organic chemicals have also been detected in the plumes.
Together, the results point to an environment that at least offers the possibility of a place where life could dwell.
The icy grains forming Saturn's E-ring were studied by a European instrument on the American space agency Nasa's Cassini spacecraft.
Cassini first detected the Enceladus water jets in July 2005.
A team led by Dr Frank Postberg, from the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, wrote in the journal Nature: "Alkaline salt water, together with the observed organic compounds and the thermal energy obviously present in the south polar region, could provide an environment well suited for the formation of life precursors."
Cassini's Cosmic Dust Analyser instrument found that about 6% of the grains forming the E-ring were rich in sodium salts. This could only have arisen if the plumes feeding the ring originated from salty water, said the scientists.
The picture is complicated by separate ground-based observations, also reported in Nature, showing no sign of sodium in the plumes themselves.
But this would not be surprising if the salty water was evaporating slowly in pressurised underground chambers rather than explosively in a vacuum, say the scientists.
Dr Postberg said: "The original picture of the plumes as violently erupting Yellowstone-like geysers is changing. They seem more like steady jets of vapour and ice fed by a large water reservoir. However, we can't decide yet if the water is currently 'trapped' within huge pockets in Enceladus' thick crust ice or still connected to a large ocean in contact with the rocky core."
Further data from Enceladus is expected to come from two more Cassini flybys in November.
Commenting on the research in Nature, US planetary scientist Dr John Spencer, from the Southwest Research Institute in Boulder, Colorado, wrote: "Many more discoveries are.. likely, and with each Enceladus becomes more exotic.
"Our picture of its subsurface must now be expanded to include the possibility of misty ice caverns floored with pools and channels of salty water, lurking beneath the tiger stripes. What else may lurk in those salty pools, if they exist, remains to be seen."
Enceladus from Voyager 2
A report published in the scientific journal ''Nature'' of results from the Cassini probe indicates the discovery  of the existence of liquid water on Saturn's moon Enceladus, and with it the possibility of extraterrestrial life.

Analysis of ice particles once thought to be emitted by geysers from the moon revealed the presence of sodium salt in the ice. As on Earth, the most plausible explanation of the presence of salt water is the prolonged contact of liquid water with mineral bearing rocks.
 
The currently accepted scientific theory for how life occurs requires the presence of three elements: the existence of complex organic molecules, liquid water and a source of energy. All three appear to be present on Enceladus.

The possibility of discovering a global ocean on the moon has receded, and has been replaced by the idea of large subterranean caverns with large pools or lakes of water, created by tidal forces acting upon Enceladus, and it is from these mist filled caverns that the water evaporates into the atmosphere in a steady jet. However, until further flybys and missions can be carried out other mechanisms for the presence of salt water ice cannot yet be dismissed.