Enceladus, the sixth largest of Saturn’s moons, is known for spraying tiny particles of icy silica, so many that the particles are a key component of the second outermost ring around Saturn. Scientists have not known how that happens or how long the process takes. A study led by UCLA scientists shows that tidal heating in Enceladus’s core creates currents that carry silica, which is likely to be released from deep-sea hydrothermal vents over the course of a few months. Credit: NASA
Cassini found substantial amounts of hydrogen gas in the plumes, which, along with the silica, present convincing evidence of hydrothermal activity on the ocean floor.
Although relatively small, Enceladus, the sixth largest of Saturn’s 83 moons, is considered by astronomers to be one of the most fascinating bodies in our solar system.
Enceladus is distinguished from other celestial bodies both by its appearance and its behavior. It has the whitest, most reflective surface astronomers have so far observed. And it’s known for spraying out tiny particles of icy silica, so many of them that the particles are a major component of the second outermost ring around Saturn, its so-called E ring.
Enceladus is characterized as an “ocean world,” a celestial body with a substantial volume of liquid water. But unlike Earth’s oceans, which lie on the planet’s surface, Enceladus’s ocean is protected under a thick layer of ice. However, the ice does not completely trap the ocean: some material from the watery expanse is released near Enceladus’s warmer south pole from large fractures in the ice known as “tiger stripes.”
The silica particles ejected by Enceladus begin their journey at the bottom of the sea, deep below the moon’s surface, and to date, scientists don’t know how this happens or how long the process takes.
A new study led by UCLA scientists offers some answers. The research shows that tidal heating in Enceladus’s rocky core creates currents that carry the silica, which is likely to be released from deep-sea hydrothermal vents over the course of a few months.
The research was published in Communications Earth & Environment.
Ashley Schoenfeld, a doctoral student in planetary sciences at UCLA, led a group that analyzed data about Enceladus’s orbit, ocean, and geology that had been collected by NASA’s Cassini spacecraft. The scientists built a theoretical model that could explain the transport of silica across the ocean.
Enceladus’ active geology is powered by tidal forces as it orbits Saturn: gravity tugs and crushes the moon. That deformation creates friction on both the moon’s ice shell and its deep rocky core. The new model showed that friction warms the ocean floor enough to create a current that carries the silica particles to the surface.
“Our research shows that these flows are strong enough to pick up materials from the seafloor and carry them to the ice sheet that separates the ocean from the vacuum of space,” Schoenfeld said. “The tiger stripe-shaped fractures that cut through the ice sheet in this subterranean ocean can act as direct conduits for captured materials to be spewed into space. Enceladus is giving us free samples of what lurks in the depths.”
Cassini found substantial amounts of hydrogen gas in the plumes, which, along with the silica, present convincing evidence of hydrothermal activity on the ocean floor. The theoretical model devised by the UCLA-led team bolsters that hypothesis by demonstrating a plausible time frame for the process and a compelling mechanism that would explain why the plumes contain silica. The model would also help explain why other materials are transported to the surface, along with the silica particles.
“Our model provides further support for the idea that convective turbulence in the ocean efficiently transports vital nutrients from the seafloor to the ice sheet,” said second author Emily Hawkins, a UCLA alumnus who is now an assistant professor of physics at Loyola Marymount University.
On Earth, similar deep-sea hydrothermal vents are home to a multitude of fascinating organisms that feast on the minerals the vents release.
In the future, the spacecraft could collect more data to allow scientists to further study the physical and chemical properties of Enceladus’ possible hydrothermal vent systems. To determine whether those vents could support life, scientists would have to analyze the plumes for chemical traces of biological activity, known as biosignatures; the new study offers some guidance that should help in the search for those biosignatures.