The fortuitous lighting of Saturn's equinox has revealed the planet's famously smooth, flat rings are actually corrugated.

During the days immediately after the August 11 equinox, the sun's rays struck the rings at very low angles, bringing their topography into high-relief.

For scientists studying the rings, the event happening once every 15 years provided an unprecedentedly dimensional view of the rings.

They were thought to be about 30 feet thick — and they are, generally speaking — but the Cassini spacecraft has revealed regions that are nearly two miles high.

"Like the seas of Earth, this wide icy expanse has settled into a mathematically precise cast that, here and there, froths and churns, not by wind but by the convulsive forces of Saturnian moons," Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, wrote in her Captain's Log. "This famous adornment, impressed deep in the human mind for four centuries as a pure, two-dimensional form, has now, as if by trickery, sprung into the third dimension."

There are several different types of clumps and corrugations and walls within the rings. Scientists have different theories about how the structures might form. Some of them, they know, are caused by Saturn's moons.

"It turns out that as the orbits of the moons are a little inclined relative to the ring plane, they pull the particles out of the plane," said Linda Spilker, Cassini deputy project scientist at the Jet Propulsion Laboratory in Pasadena, California.

In the picture above, the ring mountains can be seen at the upper right casting a shadow on the gray ring to the right. They were pulled up out of the ring plane by the moon Daphnis.

Other structures seen in the rings are more mysterious. Corrugationsacross the C and D rings could have been caused by a collision with some kind of space object, but Spilker said the Cassini team isn't sure about that.

In general, the scientists were surprised by the amount of height variation within the rings, most of which they were only able to see because of the good timing of the mission.

"It was very lucky that we had Cassini at the rings at the right time," Spilker said.

The image at the top of the post shows Saturn a day and a half after the equinox. It has been enhanced to increase the drama of the view, and Porco provided a wonderfully detailed explanation of how the image was created.

"To improve their visibility, the dark (right) half of the rings has been brightened relative to the brighter (left) half by a factor of three, and then the whole ring system has been brightened by a factor of 20 relative to the planet," Porco wrote. "So the dark half of the rings is 60 times brighter, and the bright half 20 times brighter, than they would have appeared if the entire system, planet included, could have been captured in a single image."

Images: NASA/JPL/Space Science Institute.

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