We Might Now Know How Enceladus Keeps Its Liquid Ocean

Tidal heating in the rocky core may explain the liquid ocean. NASA/JPL-Caltech

Jonathan O`Callaghan 06 Nov 2017, 16:00

Scientists have made an exciting discovery about Saturn’s moon Enceladus that may explain how its ocean is able to remain liquid.

In a paper in Nature, researchers suggest that the core of the moon may be porous – and this may dissipate heat throughout the ocean in a unique way unseen elsewhere in the Solar System.

It’s thought that the gravitational push and pull of Saturn and the other moons may cause tidal heating in the rocky core. The liquid water then routinely enters and exits the core, spreading warmer water throughout the moon.

This remarkable mechanism could explain how the moon maintains a global ocean, and why its icy shell varies so much in thickness.

“For the first time we have computed how much heat could be generated by tidal heating,” Gaël Choblet from the University of Nantes in France, lead author on the study, told IFLScience.

In their model, the team found that from the core, hydrothermal plumes of water measuring up to 100°C (212°F) may be entering the ocean. And the ocean is extremely efficient at moving this liquid from the sea floor to the ice shell, meaning there is a temperature variation of just 1°C (1.8°F) throughout.

We know there's a liquid ocean thanks to data from the Cassini spacecraft. However, scientists could not explain why the ocean was salty, nor how it was fed by an abnormally high heat power of 20 billion watts. This paper shows that tidal friction in the rocky core could account for at least half that power.

We know Enceladus has a liquid ocean thanks to Cassini. NASA/JPL-Caltech

Their model shows in particular that the hotspots were concentrated at the poles. This could explain why the icy shell is just 2 kilometers (1.2 miles) thick at the south pole and 10 kilometers (6.2 miles) thick at the north pole, compared to 40 kilometers (25 miles) at the equator.

“To preserve a thin icy shell, there has to be deep heat sources,” said Choblet. “Before we believed the tidal heating was dissipated within the icy shell. But that’s not possible, and that’s why for the first time [we suggest] it could be produced globally within the core.

“We can match Enceladus’ heat budget that Cassini saw at the surface, which is about 15 gigawatts.”

This process also seems to be quite unique to Enceladus. Although we think many other worlds including Europa and Pluto contain oceans, they likely have different ways of dissipating their heat that we don't yet understand.  

As for how long this process might last, the upper estimate suggests it could take place in billions of years. A lower estimate, however, suggests just tens of millions of years – which may have implications for finding life.

“We are agnostic about whether this is enough [time] for life to develop,” said Choblet.

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