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IN THE cold of space, a tiny moon is keeping warm with the help of a fluffy heart. Enceladus, the pipsqueak of a world renowned for shooting huge watery plumes into space as it orbits Saturn, has a secret 鈥� a core that contradicts everything we thought we knew about the structure of planetary bodies.
Planets and moons usually follow the classic 鈥渙nion鈥� model 鈥� an outer crust or atmosphere over a large mantle, with a sphere of dense material at the core. But new research presented at the Geological Society of America meeting in Vancouver on 19 October suggests Enceladus isn鈥檛 following the rules.
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Combined with its icy surface and penchant for spewing water and ammonia into space, the moon ought to have a crust of ice, a watery mantle and a core of solid rock. As Enceladus orbits Saturn, changes in the planet鈥檚 gravitational pull flex the moon, heating it up. But when James Roberts at Johns Hopkins University in Baltimore, Maryland, developed computer models to test just how this works, something didn鈥檛 add up.
A stiff rocky core would not flex enough to generate the heat necessary to melt the ice or explain the jets. When Roberts made the core more like a rocky snow cone than solid stone, it flexed and created enough heat to fuel the moon鈥檚 famous water jets. 鈥淓nceladus has been surprising us all along,鈥� says Roberts.
This article appeared in print under the headline 鈥淓nceladus, the cold moon with a heart of warm fluff鈥�