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The Saturn moon system is one bizarre place. Epimetheus and Janus exchange orbits once every four years. Mimas has an epically huge impact crater on one side and long, deep cracks on the other. And then there’s Dione, where frozen water from Enceladus falls like snow. 
Saturn itself has rings that are visible from Earth. We’ve known about them since ancient times. 
Results from the European Space Agency’s Herschel spacecraft, however, have shown us something totally new: Saturn is wrapped in a torus of water vapor – H2O to us earthlings. This donut-shaped ring is roughly 180 thousand miles wide, and 36 thousand miles thick. Water falls from this torus into Saturn’s upper atmosphere as rain. 
Evidence of the ring was discovered in 1997, but until the Herschel findings no one could explain how the ring got there, or why it hasn’t fallen into Saturn on its own. Water vapor is almost impossible to detect in visible light, but shows up well in infrared, which is Herschel’s forte. 
Even stranger is this: the donut-shaped water ring is supplied with water that spews out of the volcanoes on the moon Enceladus. 
We’ve known that Enceladus is a volcanically active moon for some time. Instead of lava bubbling out of the ground, however, we’ve known that water tumbles up through cracks on the surface and spews out of the calderas of her many volcanoes. It has been understood that water vapor drifting off of Enceladus falls like a misty snow on the moon Dione. But no one anticipated this latest finding. 
No other planetary system has shown this degree of interaction between moons and host planets, where one affects the weather on the other so directly. Enceladus is actually changing Saturn’s atmosphere (albeit in tiny amounts, given the miniscule amount of water vapor that eventually reaches the planet). 
The key player in this bizarre transaction is Enceladus, the water moon. She reflects nearly 100% of the sunlight that reaches her, making her one of the most reflective objects in the entire solar system. Just 300 miles wide, this tiny moon has an as-yet not understood internal heat source that keeps her water mantle liquid. Parts of her surface shows vast areas of resurfacing as water pours out of her volcanoes and freezes. Other regions are littered with boulders the size of houses, while still others feature deep, dark canyons. 
Enceladus supplies water vapor and ice for Saturn’s E-ring and creates weather on Dione. Now she’s discovered to be altering Saturn’s atmosphere. What’s next for this tiny moon? 
You can read more about Enceladus at NASA’s Planets page, and about the discovery of the water vapor torus at NASA’s News page.
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