The small moon Enceladus is constantly shooting water vapor out of its geysers. But that water isn't staying on the satellite - it's actually making its way to Saturn, making Enceladus the first known moon to shape its planet's composition.
Enceladus blasts more than 500 pounds of water vapor out of its geysers every second, and quite a bit of that ends up in space. There, it forms part of a vast, doughnut-shaped collection of water vapor around the planet Saturn. This torus of water extends out to about 10 times the radius of Saturn, but its actual width is only about one Saturn radius. Enceladus is located between that torus and Saturn, so it is able to constantly "refuel" the ring of water. We're only finding out about this torus now because it's transparent in visible wavelengths, and it took the Herschel infrared telescope to spot it.
But what about Saturn itself? Well, astronomers discovered the presence of trace amounts of water in Saturn's atmosphere back in 1997, and there was no ready explanation for how it could have possibly gotten there. Now we know - 3% to 5% of Enceladus's ejected water ends up on its mother planet. Lead researcher Paul Hartogh underscores just how unprecedented this is:
"There is no analogy to this behaviour on Earth. No significant quantities of water enter our atmosphere from space. This is unique to Saturn."
And it's not just Saturn itself that Enceladus is reshaping. It's thought that water also ends up freezing on the rings and raining down on the other moons. If water is falling anywhere in the Saturn system, it looks like Enceladus has something to do with it. Basically, if you're looking for the cosmic equivalent of Seattle, I think we just found it.