A Porous Core May Heat the Ocean of Enceladus

Study suggests the internal ocean could remain warm for billions of years

A recent study has provided new insights into how the subsurface ocean of Saturn's moon Enceladus could be sustained for billions of years.

NASA, JPL and Space Science Institute

Join Our Community of Science Lovers!

The mystery of why the ocean beneath the icy shell of Saturn's moon Enceladus did not freeze over long ago may now be solved — heat from the scraping of rock churning within the fragmented core of Enceladus could keep its underground ocean warm for up to billions of years, a new study finds.

This heat could help provide the kinds of conditions required for life to develop, according to the study.

In 2005, NASA's Cassini spacecraft discovered jets of water ice, organic molecules and other material blasting into space from giant fissures near Enceladus' south pole. Researchers suspect these jets come from an ocean "buried beneath a relatively thin ice shell 20 to 25 kilometers [12.4 to 15.5 miles] thick on average," said study lead author Gael Choblet, a planetary scientist at the University of Nantes in France. [Inside Enceladus, Icy Moon of Saturn (Infographic)]

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Enceladus is only about 314 miles (505 kilometers) wide, making it small enough to fit inside the borders of the state of Arizona. Given its tiny size and thin icy crust, one might have expected it to have cooled off rapidly after its formation and frozen solid by now. Previous research suggested that in order for Enceladus to still possess an internal ocean, a giant heat source was required, one generating more than 20 billion watts, which is about as much power put out by the Three Gorges Dam in China, the largest power station on Earth.

One possible source of this power is tidal heating. Whereas tides on Earth are caused by the gravitational pull of the moon and sun, tidal forces on Enceladus are mostly caused by Saturn, and are strong enough to significantly flex and heat its ice and rock.

Prior work suggested that Saturn's tidal effects on the icy shell of Enceladus would generate a relatively weak amount of heat. Without added warmth, this ocean should have frozen solid within 30 million years.

Now, researchers suggest this ocean keeps warm because of Saturn's tidal effects on the core of Enceladus. The scientists detailed their findings online today (Nov. 6) in the journal Nature Astronomy.

Previous research suggested Enceladus's core is made of fragmented rock. Choblet and his colleagues estimated that spaces packed with rock grains and water make up about 20 to 30 percent of the core.

"What we have in mind is not a sponge, where all the solid fragments are interconnected, but a pile of sand and gravel," Choblet told Space.com.

The scientists designed a computer model based on Cassini data that simulated the heat generated by tidal forces acting on Enceladus' porous core. They found the resulting friction between rock grains could generate more than 10 billion to 30 billion watts of heat.

The researchers added that heated water from the core could well outward and upward, generating hotspots on the floor of the buried ocean, particularly at the south pole of Enceladus. The new model can therefore explain the ocean of Enceladus as well as the activity seen at its south pole.

Choblet and his colleagues found this effect could heat Enceladus from tens of millions of years to billions of years. This may be long enough to supply the kinds of conditions needed for life to develop, they said.

EDITOR'S RECOMMENDATIONS

Subscribe to Support Independent Journalism

Great science journalism requires human expertise, time, effort and creativity. And it costs money. That’s why I and the journalists here at Scientific American hope you’ll join our community.

When you subscribe, you are supporting staff and freelance journalists who are passionate about telling science stories that are true, important and compelling. Our editors and reporters are often experts in their fields, which means they understand the nuances of big discoveries and can untangle the breakthroughs from the hype. With a subscription, you are also supporting rigorous fact-checking to ensure the words we publish are precise and accurate. And you’re supporting original illustrations, graphics and photos that bring you closer to an advanced laboratory, an ice sheet in Antarctica or a space mission in orbit. You’re helping us craft other types of high-quality journalism as well: Our newsletters are carefully written, edited and curated by staffers you have or will come to know and love. Our Science Quickly podcast is based on original reporting, collaboration with editors and scientists and exacting production.

Subscriptions keep this engine running so we can continue to deliver thoughtful, rigorous and independent science journalism to you. In an era of viral misinformation, this work is crucial. If you value what we do, I hope you’ll consider joining us as a subscriber

Thank you,

Jeanna Bryner, Editor in Chief, Scientific American