Saturn's moon Enceladus could harbour a liquid water ocean beneath its icy crust, according to data sent back by the Cassini spacecraft.
This false-colour image shows the extent of the active region (Image: Nasa/JPL/SSI)
Until Cassini reached Saturn, the tiny moon had received little attention.
But Enceladus is now the focus of intensive study following the discovery that it is geologically active.
Enceladus may possess reservoirs of near-surface liquid water that erupt to form geysers - and where there's water, there may be life, scientists argue.
These jets have been observed erupting from a "hot spot" in the moon's south polar region.
Scientists on the mission have likened them to the kinds of geysers found in Yellowstone National Park in the US.
"We realise that this is a radical conclusion - that we may have evidence for liquid water within a body so small and so cold," said Dr Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, US.
"However, if we are right, we have significantly broadened the diversity of Solar System environments where we might possibly have conditions suitable for living organisms. It doesn't get any more exciting than this."
Dr Jeffrey Kargel, from the US Geological Survey in Flagstaff, Arizona, US, believes that shifting, glacier-like tectonic plates and tidal forces could generate and trap heat to produce the activity seen on Enceladus.
His modelling also allows for a deep liquid water ocean saturated with gases such as carbon dioxide (CO2). This CO2 may either be locked up in the icy crust or may exist as an icy clathrate seafloor below the hypothesised ocean.
Other researchers on the Cassini mission say the plume at the south pole may be erupting from near-surface pockets of liquid water above 0C (32 F), like cold versions of the Old Faithful geyser in Yellowstone Park.
"There are other moons in the Solar System that have liquid water oceans covered by kilometres of icy crust," said Dr Andrew Ingersoll from the California Institute of Technology (Caltech) in Pasadena.
"What's different here is that pockets of liquid water may be no more than 10 metres below the surface."
Jupiter's icy moon Europa is also thought to host a briny ocean beneath its crust of ice. Neptune's moon Triton has an icy volcanic surface from which break forth plumes of nitrogen.
ENCELADUS 'COLD GEYSER'