Scientists say their hunt for extra-terrestrial life has been given a boost by new evidence of a massive hidden sea on Jupiter's moon Europa.
The sea - which is as big as the North American Great Lakes - is trapped below several kilometres of ice.
Researchers at the University of Texas made the discovery while studying images taken by the Galileo space craft. They found two rough areas on an otherwise smooth icy crust.
They believe the "crinkles" are caused by floating ice shelves that are collapsing into the water.
Similar features are found on Earth's Antarctic when seawater penetrates and weakens ice shelves.
Lead scientist Dr Britney Schmidt said the breach in the icy shell could drag nutrients and energy down into the water far below.
She said: "One opinion in the scientific community has been: 'If the ice shell is thick, that's bad for biology - the surface isn't communicating with the underlying ocean.'
"Now we see evidence that even though the ice shell is thick, it can mix vigorously. That would make Europa and its ocean more habitable."
American space agency Nasa is currently considering whether to send a spacecraft to Europa that is equipped with a ground-penetrating radar.
The mission could confirm whether there are sub-glacial lakes on the moon.
Robert Pappalardo of Nasa's Planetary Science Section said: "I read the paper and immediately thought, yes, that's it. That makes sense."
The research is published in the journal Nature.