Astronomers have analysed data from the Cassini space probe. As a result, they found conclusive evidence that Mimas, one of Saturn's satellites, thought to be lifeless, has a liquid ocean.
The new information was discovered thanks to libration - fluctuations in the rotation axis of the satellite indicating geological activity supporting the inner ocean. Dr Alyssa Roden, of the Southwest Research Institute, USA, said the new discovery suggests the existence of small, unseen oceanic worlds hidden beneath the surface of the celestial body. She said the discovery has become one of the most important in planetary science over the past 25 years.
Scientists suggest that oceans beneath layers of rock and ice may lurk on other satellites of giant planets, such as Europa, Titan and Enceladus. Earth-like planets with oceans on the surface must be close to their stars to maintain temperatures capable of leaving water in a liquid state. Inner water worlds are much further away from their stars. However, life may well exist in the water beneath the ice.
"Since the surface of Mimas is dotted with craters, we thought it was just a block of ice. Satellites like Enceladus and Europa tend to crack and show other signs of geological activity. It turns out that the surface of Mimas fooled us, and our new discovery has greatly expanded the definition of a potentially habitable world in our solar system and beyond," Rodin said.
The attraction of a neighbouring planet converts the orbital rotational energy in the satellite into thermal energy. This keeps the ice crust thick, but it also keeps the ocean hidden beneath its thickness from freezing. The ice cover can be 20 to 35 km thick.
The Juno spacecraft is to fly past Europa and use its microwave radiometer to measure heat flows on this Jupiter satellite. The data obtained will enable scientists to understand how heat flows and planetary gravity affect the ice shells of oceanic worlds.
