Saturn’s hexagon brings new, colorful mysteries

As if the north pole of Saturn weren’t weird enough already.

“Cassini is different — it’s a mission of enormous scope and is being conducted in grand style. It is much more sophisticated than Voyager, … I can’t say it’s got that flavor of romance, though. Voyager was very romantic. Cassini is spectacular.” –Carolyn Porco

Saturn, the farthest naked-eye planet visible from Earth, is famous for its rings, its bands and its yellow color.

Saturn as viewed by Hubble back in 1994, when its north pole was tilted towards us. It’s very difficult to make out any features, even with Hubble’s resolution. (Image credit: Reta Beebe (New Mexico State University), D. Gilmore, L. Bergeron (STScI), and NASA/ESA)

Only from spacecraft can we get a good view of its poles, as Voyager first revealed.

*Saturn’s north pole, as imaged by Voyager (L) and then by Cassini (R) decades later. (Images credit: D.A. Godfrey/NOAO (L); NASA/JPL-Caltech/Space Science Institute (R))*

Thanks to the Cassini orbiter’s confirmation, the north pole revealed a tremendous surprise: a hexagonal-shaped storm.

*A near-infrared view of the hexagon at Saturn’s north pole. (Image credit: NASA/JPL-Caltech/Space Science Institute)*

Over 32,000 km (20,000 miles) wide, the storm starts at 78º latitude and extends down for some 100 km (60 miles).

*A false-color image of Saturn’s north pole highlights the different features inside and around the hexagon, including the north polar vortex. (Image credit: NASA/JPL-Caltech/Space Science Institute)*

Unlike all other atmospheric features, the hexagon does not vary in latitude at all as time passes.

*A false-color animation of Saturn’s hexagon from about 70 individual frames stitched together. (Image credit: NASA/JPL-Caltech/SSI/Hampton University)*

An east-moving air current at 360 km/hr (220 mph) around the hexagon’s outline, combined with lower-latitude airflow, can reproduce the hexagon in computer simulations.

From 2012 to 2016, the hexagon was seen to change color, from bluish to yellow, where it now better matches the rest of Saturn’s color.

*Two four-year-apart images of Saturn’s north pole, both taken with the Cassini wide-angle camera. (Images credit: NASA / JPL / Space Science Institute)*

Cassini lacks the instruments necessary to measure the composition of the color-changing haze, but there’s a theory behind why.

*Cassini’s true-color view of the north pole before the color change occurred. (Image credit: NASA / JPL-Caltech / Space Science Institute)*

Saturn’s north pole tilted into sunlight in 2009 and has gotten warmer ever since.

*The north pole, as shown in this 2013 image, began to turn from blue to yellow slowly. (Image credit: NASA / JPL-Caltech / Space Science Institute)*

As the polar hazes heat up, their composition and ionization may change, leading to a yellow color in Saturnian summer.

*As Saturn approaches solstice in its orbit, the yellows are expected to intensify, but the hexagon should remain unchanged in structure. (Image credit: NASA / JPL-Caltech / Space Science Institute)*

Mostly Mute Monday tells the story of a single astronomical phenomenon or object in visuals, images and video in no more than 200 words.

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