Saturn's 'Boring' Moon May Be Hiding an Entire Ocean Under its Icy Crust

From a distance, Saturn’s moon Dione may look something like the Earth’s satellite: gray and static. New close up images taken by NASA’s Cassini spacecraft, however, suggest that it may have been active in the past and could still be now.

“A picture is emerging that suggests Dione could be a fossil of the wondrous activity Cassini discovered spraying from Saturn’s geyser moon Enceladus or perhaps a weaker copycat of Enceladus,” Bonnie Buratti who oversees the Cassini science team that studies icy satellites said in a press release. “There may turn out to be many more active worlds with water out there than we previously thought.”

What is going on beneath the Dione’s unassuming surface isn’t perfectly clear; however, Cassini’s magnetometer has detected a faint particle stream coming from it, and images show evidence for a possible liquid or slushy layer under its rock-hard ice crust.

Additional images taken by the spacecraft have also revealed ancient, inactive fractures at Dione similar to those seen at Enceladus currently spraying water ice and organic particles.

Other bodies believed to have a subsurface ocean besides Enceladus include Titan, another one of Saturn’s moons, and Jupiter’s Europa, all of which are among the most geologically active worlds in the solar system. As intriguing targets for geologists and scientists looking for the building blocks of life, the possibility of a subsurface ocean at Dione would boost the astrobiological potential of the “once boring ice ball,” according to researchers at NASA’s Jet Propulation Laboratory.

Janiculum Dorsa, the mountain that has served as the most recent subject of Cassini's lens, has ranges in height from 0.6 to 1.2 miles (1 to 2 kilometers). Under it is a bending crust that suggests the icy crust was once warm and, as Noah Hammond of Brown University and the study’s lead author explained, “the best way to get that heat is if Dione had a subsurface ocean when the ridge formed.”

Dione heats up as its stretched and squeezed as its orbit around Saturn that brings it closer and then farther away from the massive planet. Moreover, with an icy crust that can slide around independently of the moon’s core, the gravitational pulls become exaggerated and create 10 times more heat, Hammond said, arguing that any other explanations, such as a local hotspot, would be unlikely.

At this point, scientists are still investigating as to why Enceladus became so active while Dione seems to have merely sputtered along like the gloomy sister. And while theories abound, including stronger tidal waves or more radioactive heating on the former, Dione’s popularity is sure to increase as scientists set about discovering what is going on underneath the icy façade.