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Saturn’s rings keep growing more amazing

Two bright stars and one bright planet greet you when you look to the southeastern sky these evenings. You can see them even through city skyglow.

The brightest and highest is Arcturus, the “Spring Star.” It is colored like a drop of ginger ale splashed high from some backyard barbecue.

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Look to its lower right by about three fist-widths at arm’s length and there’s Spica, twinkling like an ice chip with just a trace of blue.

Look a fist and a half lower left from Spica, and you’ll find the planet Saturn. It doesn’t twinkle at all, but glows steadily yellow-white. If buildings or trees block Saturn from your view after nightfall, wait a bit. The whole huge triangle — ­Arcturus, Spica, and Saturn — rises higher as night grows late.

Galileo, using his first blurry telescopes in 1610, saw that something was vaguely amiss with Saturn. He guessed that it had two smaller balls almost touching it on either side. By 1616 he was describing Saturn as having handles like a jug. Not until 1655 did someone get it right. Saturn, said the Dutch telescope maker Christiaan Huygens, “is surrounded by a thin, flat ring, nowhere ­attached.”

Today a good backyard scope shows three rings with different brightnesses. Two are separated by a thin line.

Long before spaceflight, astron­omers figured out that the rings were not just weird, but breathtakingly weird. They were 170,000 miles wide but only several yards thick. They were made mostly of pure ice. They could not be solid sheets but had to be streams of ice pebbles, snow chunks, and ice boulders, all orbiting Saturn independently, forming a vast flat plain with 100 times the surface area of Earth.

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Then in 1980 and 1981 the Voyager 1 and 2 spacecraft flew by Saturn. Their photographs revealed not just three rings but thousands. The whole plain was made of light and dark ribbons and threads finer and finer down to a few miles wide and probably less, in patterns of ­exquisite, complex, and largely unexplained detail.

Then the Cassini probe took up residence orbiting Saturn in 2004. Cassini continues working there today. It has resolved ever finer details in the ringlets and is tracking them jostling and evolving over time.

Scientists are interested in the rings of Saturn not just for their weird physics and alien beauty. The solar system itself condensed from a much larger flat disk of dust, rubble, and gas that must have had a partial resem­blance to Saturn’s rings now. This is how planets form around almost all newborn stars. At some stars we can ­detect disks remaining. Around most stars nothing remains ­except for, presumably, the planets and smaller bodies they birthed.

So astronomers are coming to think that the strange and abundant processes we see happening in Saturn’s rings are probably telling something about how the material of Earth, and all other planets, worked its way into the worlds we have.

Alan M. MacRobert is a senior editor of Sky & Telescope magazine (SkyandTelescope.com). His Star Watch column ­appears the first Saturday
of every month.

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