New images from NASA's Cassini spacecraft suggest that Saturn's moon Dione may have once had a geologically active subsurface ocean.
Images of Dione's 800-kilometres-long mountain Janiculum Dorsa suggest that the moon may have once been very similar to its sister moon - Enceladus.
"There may turn out to be many more active worlds with water out there than we previously thought," said Bonnie Buratti, who leads the Cassini science team at NASA's Jet Propulsion Laboratory in Pasadena, California.
Other bodies in the solar system thought to have a subsurface ocean - including Saturn's moons Enceladus and Titan and Jupiter's moon Europa - are among the most geologically active worlds in our solar system.
They have been intriguing targets for geologists and scientists looking for the building blocks of life elsewhere in the solar system.
The presence of a subsurface ocean at Dione would boost the astrobiological potential of this once-boring iceball.
Cassini, which has been exploring Saturn since 2004, detected a weak particle stream coming from Dione with its magnetometer, LiveScience reported.
Images taken by the spacecraft suggest a slushy liquid layer might exist beneath its icy crust, as well as ancient, inactive fractures that now spew water ice and carbon-containing particles, much like ones seen on Enceladus.
Dione's Janiculum Dorsa ranges from about 1 to 2 kilometres in height. The mountain seems to have deformed the icy crust underneath by as much as 0.5 kilometre.
"The bending of the crust under Janiculum Dorsa suggests the icy crust was warm, and the best way to get that heat is if Dione had a subsurface ocean when the ridge formed," said Noah Hammond, the paper's lead author, who is based at Brown University.
Dione gets heated up by being stretched and squeezed as it gets closer to and farther from Saturn in its orbit. With an icy crust that can slide around independently of the moon's core, the gravitational pulls of Saturn get exaggerated and create 10 times more heat, Hammond explained.
Other possible explanations, such as a local hotspot or a wild orbit, seemed unlikely.
The findings were published in the journal Icarus.
