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Huge “hidden” Saturn ring found

Oct. 7, 2009
Courtesy Nature
and World Science staff

Ob­serva­t­ions from a space tel­e­scope have re­vealed the largest-known plan­e­tary ring in the So­lar Sys­tem, as­tro­no­mers re­port.

The subtle, new­found ring sur­rounds the ga­seous plan­et, but much fur­ther out than its fa­mil­iar, more vis­i­ble rings, scientists said; if it were were vis­i­ble from Earth, the ring’s full cir­cle would ap­pear to be twice the size of the our Moon.

Sat­urn's moon Iap­e­tus. As­tro­no­mers pro­pose is dark­ly col­ored on one side be­cause of dust from a new­ly dis­cov­ered ring of Sat­urn. (Im­age cour­te­sy Cas­si­ni Im­ag­ing Team, SSI, JPL, ESA, NA­SA )

The ring is as­so­ci­at­ed with Sat­urn’s dis­tant moon Phoe­be, which or­bits the gi­ant plan­et about 13 mil­lion kilo­me­tres (8 mil­lion miles) away. That is roughly 200 times Sat­urn’s ra­di­us, or dis­tance from its cen­ter to its sur­face.

Un­til now, the largest-known plan­e­tary rings were Jupiter’s gos­sa­mer rings and Sat­urn’s E ring — sheets of dust that ex­tend to about 5 to 10 times the ra­di­us of their re­spec­tive plan­ets. 

The new find­ings, made us­ing NA­SA’s Spitzer Space Tel­e­scope, are de­scribed in the Oct. 8 is­sue of the re­search jour­nal Na­ture. As­tro­no­mers Anne Ver­bis­cer of the Un­ivers­ity of Vir­gin­ia and col­leagues, who re­ported the find, al­so pre­sented sim­ula­t­ions show­ing how dust in the ring could come from re­peat­ed im­pacts of ob­jects strik­ing Phoe­be.

An artist's con­cep­tion si­mu­lat­ing an in­fra­red view of the gi­ant ring sur­round­ing Sa­turn. Sa­turn it­self is just a dot, en­larged in the in­set im­age. (NA­SA / JPL-Cal­tech / Keck)

The new­found ring is tilted 27 de­grees with res­pect to the main rings, re­search­ers said.

The faint but enor­mous ring may al­so ex­plain a long­stand­ing mys­ter­y: the two-tone col­ora­t­ion of an­oth­er Sat­urnian moon, Iap­e­tus, Ver­bis­cer and col­leagues pro­posed. One side of Iap­e­tus is darker than the oth­er, lead­ing to sug­ges­tions that the front face might be coat­ed with dust spi­ral­ling in from Sat­urn’s darker out­er moons, in­clud­ing Phoe­be.

Ver­bis­cer and col­leagues cal­cu­late that, over the his­to­ry of the So­lar Sys­tem, ma­te­ri­al from the ring could have sup­plied Iap­e­tus’s front face with a blan­ket of dark dust a few me­tres (yards) thick.

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Observations from a space telescope have revealed the largest-known planetary ring in the Solar System, astronomers report. The ring surrounds Saturn, but much further out than its familiar, more visible rings. If it were were visible from Earth, it would form a circle that would appear to be twice the size of the our Moon, scientists said. The newly discovered ring is associated with Saturn’s distant moon Phoebe, which orbits the giant planet about 13 million kilometres (8 million miles) away. That is roughly 200 times Saturn’s radius, or distance from its center to its surface. Until now, the largest-known planetary rings were Jupiter’s gossamer rings and Saturn’s E ring — sheets of dust that extend to about 5 to 10 times the radius of their respective planets, according to astronomers. The findings, made using NASA’s Spitzer Space Telescope, are reported in the Oct. 8 issue of the research journal Nature. Astronomers Anne Verbiscer of the University of Virginia and colleagues, who reported the find, also presented simulations showing how dust in the ring could come from repeated impacts of objects striking Phoebe. The faint but enormous ring may also explain a longstanding mystery: the two-tone coloration of another Saturnian moon, Iapetus, Verbiscer and colleagues proposed. One side of Iapetus is darker than the other, leading to suggestions that the front face might be coated with dust spiralling in from Saturn’s darker outer moons, including Phoebe. Verbiscer and colleagues calculate that, over the history of the Solar System, material from the ring could have supplied Iapetus’s front face with a blanket of dark dust a few metres (yards) thick.