Saturn, the second-largest planet in the Solar System after Jupiter, has always attracted the attention of not just scientists but also amateur astronomers. Given the prominent rings around it, it is easily recognisable. But it has another outstanding feature: more than 60 moons. One of these moons has got scientists particularly interested recently. According to new research, Mimas, a tiny moon orbiting the planet, could be hiding an ocean under its frozen surface.

Not surprising, Saturn itself is the only planet that is less dense than water, meaning if there were a bathtub big enough to hold it, the Ringed Planet would float. Mimas has a wobbly rotation and scientists believe it is suggestive of an elongated core or an internal ocean.

However, unlike other moons with oceans, Mimas has no markers on its surface indicating an ocean underneath. The research, published in the Icarus journal, says it could be. Like many other scientists, researchers Alyssa Rhoden had set out to disprove the ocean hypothesis when she and her colleague Matthew Walker realised it might actually hold water beneath 14–20 miles of ice.

Rhoden, a specialist in the geophysics of icy satellites and co-leader of NASA’s Network for Ocean Worlds Research Coordination Network, said because the surface of Mimas is heavily cratered, she and her colleague thought it was just a frozen block of ice. Rhoden said in a press release that Mimas’ surface has been deceiving researchers all along, and their new knowledge has dramatically broadened the notion of a potentially habitable world in the solar system and beyond.

Rhoden added that while their findings support the existence of a present-day ocean within Mimas, it was difficult to reconcile the “moon’s orbital and geologic characteristics with our current understanding of its thermal-orbital evolution.”

She added evaluating Mimas’ status as an ocean moon would help researchers better understand Saturn’s rings and mid-sized moons.