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NASA’s Cassini spacecraft discovered that Enceladus, a small moon circling Saturn, has dozens of icy geysers erupting from cracks near its south pole that shoot plumes of mineral-laden water ice and water vapour into space. Cassini’s science instruments also detected a global, salty ocean underneath Enceladus’ icy crust that is the source of these geysers. This moon, only 480 kilometres (300 miles) across, is extremely cold and should have frozen solid long ago. However, something is keeping the ocean from freezing and turning Enceladus into a frozen ball of ice.
One explanation is that Enceladus’ orbit is not a perfect circle, but is slightly eccentric, moving Enceladus closer to and farther from Saturn as it orbits the planet. This slight difference in distance to Saturn results in a tidal flexing of Enceladus, heating its interior. Perhaps the key to additional heat may lie in Enceladus’ core. If this core is not solid, rocky material, but is instead porous, it could allow water to circulate through it. Tidal flexing could then cause rocky material to grind together, generating frictional heat that heats the water and creates hot spots on the ocean floor. All this excess heat helps maintain Enceladus’ liquid-water ocean. Linda Spilker is project scientist of NASA’s Cassini mission that explored the Saturnian system