Enceladus’s hot, gritty core may cook up ingredients for life

By Leah Crane

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.

The core is constantly flexing because of tidal forces created by Saturn’s gravity that heat up the centre of Enceladus. It seems that as water flows through pores and cracks among the grains, it warms, possibly even getting hot enough to boil. It then shoots out of the core into the ocean above in a narrow underwater geyser.

Because of the geometry of Enceladus’s orbit around Saturn, more of this hot water ends up moving towards the moon’s poles, heating and thinning the underside of the ice in both spots.

“Even though there were no active jets observed at the north pole during the Cassini mission, there is a possibility that we will observe some sort of activity at the north pole in the future,” says Choblet.

Chemical bake

The heating of the ocean water as it cycles through the core may also help provide the energy needed to form complex molecules necessary for life. “The kitchen is open, basically,” says Christopher Glein at the Southwest Research Institute in San Antonio, Texas. “The core is where all the ingredients for interesting chemistry are being baked.”

These ingredients include the white silica particles that Cassini found in Enceladus’s plumes. Glein says these could float in the water and coat the core and any mineral towers growing near hydrothermal vents, creating a pale, eerie scene.

What’s more, Choblet and his team found that the tidal heating effect could persist for tens of millions to billions of years, giving any potential life plenty of time to evolve in the resulting warm, chemically diverse areas.

Glein says the possible cracks in the sea floor might even give fish or other small life forms a convenient place to hide. “It’s probably going to look like earthquake city down there in the core,” he says. “That’s where the fish would be hiding, in the huge faults… well, if there are fish on Enceladus.”

Journal reference: Nature Astronomy, DOI: 10.1038/s41550-017-0289-8

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Chemical bake