Cassini Week: Rings

In the famous words of the 21st Century philosopher, Beyoncé, “if you like it then you shoulda put a ring on it”.

In that case, the Universe must have really liked Saturn.

While all of the gas giants in our solar system have rings, Saturn’s are by far the most prominent and celebrated. And while humans have been admiring Saturn’s rings for centuries (when Galileo first discovered them, he described them as Saturn’s ears), it was Cassini that brought them into razor-sharp focus.

Shadows cast on Saturn's A ring.

Shadows cast on Saturn’s A ring. – Credit: NASA/JPL/Space Science Institute

Several sets of shadows are cast onto the A ring in this image taken about a week after Saturn’s August 2009 equinox.

Near the middle of the image, shadows are cast by vertically extended clumps in the kinky, discontinuous ringlets of the Encke Gap in the A ring. These clumps are casting shadows approximately 275 kilometers (170 miles) long, implying a clump height about 600 meters (2,000 feet) above the ring plane.

In the middle left of the image, the waves created by Daphnis (8 kilometers, 5 miles across) on the edge of the Keeler Gap cast shadows on the A ring that are about 450 kilometers (280 miles) long, indicating waves that rise about one kilometer above the ring plane. The moon itself is not visible at this resolution, but it, too, orbits in the Keeler Gap of the A ring. Daphnis has an inclined orbit, and its gravitational pull perturbs the orbits of the particles of the A ring forming the Keeler Gap’s edge and sculpts the edge into waves having both horizontal (radial) and out-of-plane components. Material on the inner edge of the gap orbits faster than the moon so that the waves there lead the moon in its orbit. Material on the outer edge moves slower than the moon, so waves there trail the moon.

The Janus 2:1 spiral density wave

The Janus 2:1 spiral density wave – Credit: NASA/JPL-Caltech/SSI

This view from NASA’s Cassini spacecraft shows a wave structure in Saturn’s rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn’s rings are much more tightly wound. In this case, every second wave crest is actually the same spiral arm which has encircled the entire planet multiple times.

Propeller in Saturn's A Ring

Propeller in Saturn’s A Ring – Credit: NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini spacecraft captured these remarkable views of a propeller feature in Saturn’s A ring on Feb. 21, 2017. These are the sharpest images taken of a propeller so far, and show an unprecedented level of detail. The propeller is nicknamed “Santos-Dumont,” after the pioneering Brazilian-French aviator.

Have you heard of Saturn’s propellers before? They’re the result of a very small moon, unseen in the photo above, disturbing ring material. They offer a unique opportunity for researchers to track the orbits of unseen objects that are embedded within a disk of material.

Epimetheus and smog-enshrouded Titan, with Saturn's A and F rings stretching across the scene.

Epimetheus, Titan, and rings. – Credit: NASA/JPL/Space Science Institute

Cassini delivers this stunning vista showing small, battered Epimetheus and smog-enshrouded Titan, with Saturn’s A and F rings stretching across the scene.

Stay tuned for more, as we continue our Cassini Week celebration.

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