Colour and structure in the rings of Saturn

Nasa/jpl-caltech/space science institute
A close-up view of the rings of Saturn.
NASA/JPL-Caltech/Space Science Institute

This is one of the highest-resolution color images of any part of Saturn’s rings to date, showing a portion of the inner-central part of the planet’s B Ring. The view is a mosaic of two images that show a region that lies between 98,600 and 105,500 kilometres from Saturn’s center.

This image is a natural color composite, created using images taken with red, green and blue spectral filters. The pale tan color is generally not perceptible with the naked eye in telescope views, especially given that Saturn has a similar hue. 

The material responsible for bestowing this color on the rings – which are mostly water ice and would otherwise appear white – is a matter of intense debate among ring scientists that will hopefully be settled by new in-situ observations before the end of Cassini’s mission. 

The different ringlets seen here are part of what is called the “irregular structure” of the B ring. Cassini radio occultations of the rings have shown that these features have extremely sharp boundaries on even smaller scales (radially, or along the direction outward from Saturn) than the camera can resolve here. Closer to Saturn, the irregular structures become fuzzier and more rounded, less opaque, and their color contrast diminishes. 

The narrow ringlets in the middle of this scene are each about 40 kilometres wide, and the broader bands at right are about 300 to 500 kilometres across. It remains unclear exactly what causes the variable brightness of these ringlets and bands – the basic brightness of the ring particles themselves, shadowing on their surfaces, their absolute abundance, and how densely the particles are packed, may all play a role. 

Observations from the Voyager mission and Cassini’s visual and infrared mapping spectrometer previously showed these color variations at lower resolution, but it was not known that such well-defined color contrasts would be this sharply defined down to the scale (radial scale) of a couple of kilometres, as seen here.

This image was taken on July 6, 2017, with the Cassini spacecraft narrow-angle camera. The image was acquired on the sunlit side of the rings from a distance of 76,000 kilometres away from the area pictured. The image scale is about 3 kilometres per pixel. The phase angle, or sun-ring-spacecraft angle, is 90 degrees.

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