Beneath Enceladus’s icy shell, deep under its global sea, seems to be a core made of wet sand. Water may heat up while flowing through the core’s nooks and crannies, becoming a promising environment for life.

Observations from NASA’s Cassini spacecraft indicated that something deep within this icy moon of Saturn is generating heat and fuelling the hotspots where plumes of liquid spew out of Enceladus’s south pole. But we were unsure exactly how the heat was generated.

Gaël Choblet at the University of Nantes in France and his colleagues simulated conditions on Enceladus and found that it probably has a porous, sandy core that acts as a heat source.

We know from Cassini’s measurements that the core of Enceladus is not very dense, which means the metal and rock that make up its innards must be porous. And with an ocean above, that water may be able to seep down into the core.

“Whatever the core’s composition in terms of rocks, it has to have water within it – maybe 20 or 30 per cent water,” says Choblet. That means it seems not to be formed of a single solid rock, but instead a clump of sandy or gravelly grains.

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