Mysterious silica ejected in huge quantities from Saturn’s icy moon Enceladus is powerful new evidence pointing to heat vents at the bottom of a global ocean.
According to a new analytical model, the internal heating of the moonThe core creates ocean currents that carry the silica particles, which are ejected from deep-sea hydrothermal vents that also release heat into the surrounding waters.
It’s a tantalizing discovery that teases a real possibility of the existence of life, deep within an alien ocean on an alien world.
When the Cassini spacecraft spent its years orbiting and studying Saturn, it made a startling discovery. The planet’s E ring – the second outermost of the vast ring system – has a composition rich in microscopic grains of silica, alongside ices of water, ammonia and carbon dioxide.
We have also detected silica particles from Enceladus in the form of icy plumes which spring from the fissures of the thick icy shell of the moon; scientists have determined that the composition of the E ring is provided by EnceladusSince its rocky core. And the chemistry and grain size suggest high temperatures.
But how the silica arrives from Enceladus’ core, across the deep global ocean, to be ejected through the ice in plumes has been something of a puzzle.
Enceladus is a marvel. The moon is covered with a large shell of ice, on average between 18 and 22 kilometers (11 and 14 miles) thick. But its orbit around Saturn is not perfectly round, but elliptical, which means that its distance from the planet varies, as does the force of gravity between them. This varying gravity stretches and compresses Enceladus, creating heating in its core.
Beneath the ice shell, therefore, is a global liquid ocean. more than 10 kilometers deep, and the heat emanating from the core prevents the water from freezing. It also raises the possibility of hydrothermal ventscracks in the seabed through which heat escapes from the moon’s interior.
Previous search suggested that the heat from the interior of Enceladus should generate vertical convection currents in the ocean, similar to those observed on Earth. Now, a team of planetary scientists led by Ashley Schoenfeld of the University of California, Los Angeles, has created a model involving these currents to try to understand silica transport on Enceladus.
“It’s like boiling a pot on a stove. The friction of the tides adds heat to the ocean and causes hot water currents.” Schoenfeld explains.
“What our study shows is that these flows are strong enough to pick up material from the seafloor and bring it to the shell of ice that separates the ocean from the vacuum of space. tiger stripe fractures that pass through the ice shell in this subterranean ocean can serve as direct conduits for captured materials to be hurled into space. Enceladus gives us free samples of what lies deep below.”
The implications are quite exciting. As previous research has foundsilica and other materials detected by Cassini in plumes from Enceladus, are consistent with what might be found in and at hydrothermal vents.
Here on Earth, hydrothermal vents teem with life, even far beyond the reach of sunlight. Entire ecosystems thrive on a chemosynthetic food webharnessing the chemical reactions of elements interacting at high temperatures to produce energy, rather than the more common photosynthetic processes that rely on sunlight.
This has led astrobiologists to speculate that ice moons like Enceladus could harbor life, even though they are far from the Sun, and the ocean floor receives no vital sunlight.
The new study adds to a growing body of evidence that suggests whether there are hydrothermal vents on Enceladus, and, if there is life there, then we may be able to detect it without having trying to break into the ice. An orbiter or lander – several of which are currently under study – might be able to find biomolecules on the moon’s icy surface.
“Our model” says planetary scientist Emily Hawkins from Loyola Marymount University, “provides further support for the idea that convective turbulence in the ocean efficiently transports vital nutrients from the seafloor to the ice shell”.
And isn’t that an intriguing notion? We may need to change his name to Enticingeladus.
The research has been published in Earth & Environment Communications.