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Tiny planet found to have Saturn-like rings

March 31, 2014
Courtesy of the Niels Bohr Institute -
University of Copenhagen
and World Science staff

A mini-plan­et in our so­lar sys­tem has rings, con­tra­dict­ing a long­time as­sump­tion that only big plan­ets can have these, a study finds.

The ob­ject, called Chariklo, lies two bil­lion kilo­me­ters (1.2 bil­lion miles) out in the so­lar sys­tem be­tween Ura­nus and Sat­urn—the plan­et most fa­mous for its rings, al­though faint­er rings are seen around oth­er gi­ant plan­ets: Ju­pi­ter, Ura­nus and Nep­tune.

Art­ist's con­cep­tion of Cha­rik­lo. (Cre­dit: Lucie Ma­quet)


Chariklo, which would barely fit one of the Great Lakes on its sur­face, has two rings of ice and peb­bles, ac­cord­ing to the au­thors of the new re­search, at the Niels Bohr In­sti­tute at the Uni­vers­ity of Co­pen­ha­gen. Their find­ings are pub­lished in the sci­en­tif­ic jour­nal Na­ture.

Chariklo once was in the Kuiper Belt, a group of thou­sands of dwarf plan­ets and comets in or­bit be­yond Nep­tune on the edge of our so­lar sys­tem, as­tro­no­mers said. But at some point it was thrown out of this belt and is now be­tween Sat­urn and Ura­nus, where there is a col­lec­tion of small ob­jects, called Cen­taur. Chariklo is the larg­est of these, 250 km (160 miles) wide. 

Chariklo, which is comet-like in some re­spects, has been known for many years, but its rings had gone un­seen be­fore a new cam­era started be­ing used on a Dan­ish tel­e­scope at the Eu­ro­pe­an South­ern Ob­ser­va­to­ry’s La Silla Ob­serv­a­to­ry in Chil­e.

“The cam­era was spe­cially de­vel­oped at the Niels Bohr In­sti­tute and has a stun­ningly high res­o­lu­tion, which we espe­cially ex­ploit to look for exoplan­ets,” or plan­ets out­side our so­lar sys­tem, said Uffe Gråe Jør­gensen, an as­tron­o­mer at in­sti­tute. “But when the ar­ea where we are look­ing for exoplan­ets is­n’t ‘up’ in the sky, we use our ob­serva­t­ion time for oth­er pro­jects and so we fol­lowed Chariklo, which just passed in front of a star.”

He ex­plained that when an ob­ject passes in front of a star there is a small dip in the star’s bright­ness and they could see that there was al­so a dip in the bright­ness out­side the ob­ject. This showed that there was a ring of ma­te­ri­al in a disc around the lit­tle ob­ject, Chariklo.

“We were not even look­ing for rings, be­cause they had nev­er been ob­served around small ob­jects like Chariklo, so it is a to­tally sur­pris­ing dis­cov­ery. The en­tire pas­sage only lasted 5 sec­onds, but we could even de­ter­mine in­cred­i­ble de­tails about the rings. There are two sep­a­rate thin rings, which are com­prised of ice par­t­i­cles and peb­bles. The two rings are only 3 and 7 km [a­bout 2 and 4 miles] wide and no more than a few hun­dred me­ters [yards] thick.”

The rings may have formed because another body crashed into Cha­rik­lo and tossed out some ma­terial, he added; this is what hap­pened to Earth 4.5 bil­lion years ago, lead­ing to the form­ation of the Moon. Cha­riklo's rings could also con­dense into a moon, which would be expected to be a minu­scule 2 km (1.2 miles) wide, he add­ed.  

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A mini-planet in our solar system has rings, contradicting a longtime assumption that only big planets can have these, a study finds. The object, called Chariklo, lies two billion kilometers (1.2 billion miles) out in the solar system between Uranus and Saturn—the planet most famous for its rings, although fainter rings are seen around other giant planets Jupiter, Uranus and Neptune. Chariklo, which would barely fit one of the Great Lakes on its surface, has two rings of ice and pebbles, according to the authors of the new research, at the Niels Bohr Institute at the University of Copenhagen. Their findings are published in the scientific journal Nature. Chariklo once was in the Kuiper Belt, a group of thousands of dwarf planets and comets in orbit beyond Neptune on the edge of our solar system, astronomers said. But at some point it was thrown out of this belt and is now between Saturn and Uranus, where there is a collection of small objects, called Centaur. Chariklo is the largest of these, 250 km (155 miles) wide. Chariklo, which is comet-like in some respects, has been known for many years, but its rings had gone unseen before a new camera started being used on a Danish telescope at the European Southern Observatory’s La Silla Observatory in Chile. “The camera was specially developed at the Niels Bohr Institute and has a stunningly high resolution, which we especially exploit to look for exoplanets,” or planets outside our solar system, said Uffe Gråe Jørgensen, an astronomer at institute. “But when the area where we are looking for exoplanets isn’t ‘up’ in the sky, we use our observation time for other projects and so we followed Chariklo, which just passed in front of a star.” He explained that when an object passes in front of a star there is a small dip in the star’s brightness and they could see that there was also a dip in the brightness outside the object. This showed that there was a ring of material in a disc around the little object, Chariklo. “We were not even looking for rings, because they had never been observed around small objects like Chariklo, so it is a totally surprising discovery. The entire passage only lasted 5 seconds, but we could even determine incredible details about the rings. There are two separate thin rings, which are comprised of ice particles and pebbles. The two rings are only 3 and 7 km [about 2 and 4 miles] wide and no more than a few hundred meters [yards] thick.”