Saturn’s moon Enceladus has turned out to be quite the overachiever among moons in our solar system. Only 318 miles wide — about the width of Arizona — this ice-coated world first surprised scientists in 2005 when the Cassini spacecraft spotted geysers spraying icy material from long fissures near its south pole.
Later, it was discovered that the material was mostly water ice that also contained salts and evidence of other organic compounds, strongly suggesting the presence of a salty subsurface ocean.
The fissures, nicknamed “tiger stripes”, are also emitting a surprising amount of heat — some process is keeping Enceladus’ insides warm, at least warm enough for water to remain liquid.
Later still, the Cassini team discovered that spray from Enceladus has created a giant diffuse ring around Saturn, a “halo of ice, dust and gas” that creates the planet’s hazy E ring in which the little moon resides.
Now a new finding has been announced: Enceladus rains its water onto Saturn itself, becoming the first moon known to directly influence the composition of its planet!
Way to go, Enceladus!
Earlier this summer, the European Space Agency’s Herschel Space Observatory identified the thick ring of material — called a torus — around Saturn using infrared imaging. The water making up the torus is transparent in visible light but not in infrared, which Herschel was designed to detect.
The discovery of this large band of water wrapping around Saturn in a band nearly 37,000 miles thick seemed to indicate that Enceladus is, ultimately, the source of the water identified in Saturn’s atmosphere. To help confirm this, a computer model was made.
The model worked.
Tim Cassidy, a researcher at the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder, was one of the members of the modeling team. He combined data from Herschel’s findings with models of water vapor clouds in orbit around Saturn already in development.
“What’s amazing is that the model, which is one iteration in a long line of cloud models, was built without knowledge of the (Herschel) observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren’t expecting such detailed ‘images’ of the torus, and the match between model and data was a wonderful surprise,” said Cassidy.
The team’s model showed that, although most of the water in the torus eventually dissipated into space, a small percentage of it (about 3 to 5 percent) made it into Saturn’s upper atmosphere — exactly the amount that had been previously observed by ESA’s Infrared Space Observatory and NASA’s Submillimeter Wave Astronomy Satellite (SWAS) in the late ’90s.
In addition, the model accurately predicted the rate at which Enceladus is spewing out water from its tiger stripes. Every second about 440 pounds (200 kg) of icy water vapor is ejected from Enceladus into orbit around Saturn… every second. That’s a whole lot of spraying goin’ on!
Of course, the “water” we are seeing in Saturn’s atmosphere isn’t exactly the kind you would fill a tall glass with here on Earth.
“When water hangs out in the torus, it is subject to the processes that dissociate water molecules,” said Cassini science team member Candy Hansen of the Planetary Science Institute in Tucson. “First to hydrogen and hydroxide, and then the hydroxide dissociates into hydrogen and atomic oxygen.”
It was these molecules of atomic oxygen originating from water that Cassini first saw on approach to Saturn, and now — thanks to Herschel and some very talented computer modelers — we can confidently trace the source back to Enceladus.
It’s a little moon with a big impact.
Read the news release here.
Image credit:NASA/JPL/Space Science Institute