How Planets Put a Ring on It – World Science Festival

How beautiful is a ring that sparkles, whether perched upon a finger or girdling a gas giant hundreds of millions of miles away. Like precious gems, planetary rings seem all the more beautiful for their rarity—although we’re continuing to discover that more and more bodies around us have ways of acquiring rings of their own.

While the scarcity of diamond rings is really just artificial market control, the supposed scarcity of rings in our solar system may have just been a product of not having the right tools to see them. Saturn’s rings were pinpointed by Galileo back in the early 1600s, but it wasn’t until the 1970s that Jupiter and Uranus’s ring systems were spotted; Neptune’s rings weren’t definitively confirmed until 1989. In March 2014, researchers from the European Southern Observatory spotted two dense rings encircling the asteroid Chariklo. Now, just around a year later, a team led by researchers from the Massachusetts Institute of Technology has detected rings around another minor body, Chiron.

Chiron and Chariklo both belong to a class of objects in our solar system called “centaurs,” a group of small, icy bodies located between Neptune and Jupiter. While the mythological centaurs were a hybrid of horse and man, the astronomical centaurs seem like a fusion of asteroids and comets.

The rings around Chiron—which is a pretty hefty centaur with an estimated diameter between 91 and 144 miles—might turn out to be jets of gas and dust. But the MIT team thinks their observations are indicative of two rings lying about 186 miles from Chiron’s center. More teams will have to take a look, though, to confirm the result.

Where Do the Rings Come From?

So how do rings form in the first place? In the case of both Chiron and Chariklo, the leading theories are that the material in the ring is either lingering debris from the centaur’s own formation, or perhaps captured material from the breakup of another nearby body. Planetary rings, similarly, are thought to either condense from the remains of broken-up moons (either from being smacked by asteroids or comets, or from being torn apart by tidal stresses near the planet) or to have coalesced from the protoplanetary disk of material that surrounded the sun in the solar system’s infancy. While scientists are pretty sure that Jupiter’s rings formed from dust struck off of the gas giant’s moons by tiny meteorites, for the other outer planets and centaurs, no one theory has definitively emerged as the victor.

Saturn’s bright rings are iconic, but their pristine condition has long been the source of many a frustrated head-scratching among astronomers. If the planet’s rings formed billions of years ago, the particles that make them up should have been dulled with interplanetary dust by now. But the most recent observations from the Cassini spacecraft lend weight to the idea that Saturn’s rings are really old. When a University of Colorado in Boulder team used Cassini’s instruments to measure the amount of dust passing through Saturn’s immediate vicinity, they found it much less dusty than expected. So the planet’s rings probably couldn’t have formed within a few hundred million years.

For Saturn’s rings to stay nice and sparkly, some scientists think there might be some sort of recycling system in place—perhaps the ice particles eventually form into moons, then break up to form rings again. One of Saturn’s moons, Enceladus, is currently feeding material into the planet’s E-ring from both expulsion of dust from the “tiger stripe” vents near its south pole and from clouds of material kicked up by impacts with micrometeorites.

As we continue to explore space, we may find even more rings to puzzle over. The New Horizons spacecraft, due to rendezvous with Pluto later this year, may be able to settle the question of whether or not the dwarf planet has a ring system—possibly adding yet another bright bauble to the solar system’s jewelry box.

Image Credit: Flickr CC/RDPixelShop

By: Roxanne Palmer

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