"Long before it's in the papers"
January 27, 2015


Saturn may be spawning tiny new moon

April 14, 2014
Courtesy of NASA Jet Propulsion Laboratory
and World Science staff

NASA’s Cas­si­ni space­craft has re­vealed signs of the forma­t­ion of a small icy ob­ject, pos­sibly a new moon, in Sat­urn’s rings, as­tro­no­mers say.

The ob­ject seems to be ti­ny and would probably stay that way, about a half mile (around a kil­o­me­ter) wide, they add. In­for­mally named Peg­gy, It’s too small to show up in im­ages so far, but as­tro­no­mers hope it can pro­vide clues to the forma­t­ion of Sat­urn’s known moons.

A dis­turb­ance vis­i­ble at the out­er edge of Sat­urn's A ring in this im­age from NA­SA's Cas­si­ni space­craft could be caused by an ob­ject re­play­ing the birth pro­cess of icy moons. (Im­age cour­te­sy Cas­si­ni/Huygens Mis­sion)

“We have not seen an­y­thing like this be­fore,” said Carl Mur­ray of Queen Mary Uni­vers­ity of Lon­don, lead au­thor of a re­port on the find­ings. “We may be look­ing at the act of birth, where this ob­ject is just leav­ing the rings and head­ing off to be a moon in its own right.”

That’s how some of Sa­turn’s known moons are theo­rized to have been born.

Im­ages tak­en with Cas­si­ni’s nar­row an­gle cam­era on April 15, 2013, show dis­tur­bances at the edge of Sat­urn’s A ring—the out­er­most of the plan­et’s large, bright rings. One of these dis­tur­bances is an arc about 20 per­cent brighter than its sur­round­ings, 750 miles (1,200 kil­o­me­ters) long and six miles (10 kil­o­me­ters) wide. 

The sci­en­tists al­so found un­usu­al pro­tu­ber­ances in the usu­ally smooth pro­file at the ring’s edge. Sci­en­tists think the arc and pro­tu­ber­ances re­sult from the gravita­t­ional pull of a near­by ob­ject. The re­port was pub­lished on­line April 14 in the re­search jour­nal Ic­a­rus.

The ob­ject is­n’t ex­pected to grow larg­er, and may even be fall­ing apart, as­tro­no­mers say. But they be­lieve its forma­t­ion and out­ward move­ment could help us un­der­stand how Sat­urn’s icy moons, in­clud­ing the cloud-wrapped Ti­tan and ocean-holding En­cel­a­dus, may have formed in big­ger rings long ago. It al­so of­fers in­sight in­to how Earth and oth­er plan­ets may have formed and mi­grat­ed away from our star, the sun, they add.

Sat­urn’s icy moons range in size de­pend­ing on their proxim­ity to the plan­et: the far­ther from the plan­et, the larg­er. And many of Sat­urn’s moons con­sist mainly of ice, as are the par­t­i­cles in Sat­urn’s rings. Based on these facts, and oth­er in­di­ca­tors, re­search­ers re­cently pro­posed that the icy moons formed from ring par­t­i­cles and then moved out­ward, away from the plan­et, merg­ing with oth­er moons on the way.

“Wit­ness­ing the pos­sible birth of a ti­ny moon is an ex­cit­ing, un­ex­pected event,” said Cas­si­ni Proj­ect Sci­ent­ist Lin­da Spilker, of NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Ca­lif. Ac­cord­ing to Spilker, Cas­si­ni’s or­bit will move clos­er to the out­er edge of the A ring in late 2016 and pro­vide an op­por­tun­ity to study Peg­gy in more de­tail and per­haps even im­age it.

Moon forma­t­ion in Sat­urn’s rings may be end­ing with Peg­gy, as the rings now are probably too de­plet­ed to make more moons, Mur­ray and his col­leagues said. So they’re wring­ing from the ob­serva­t­ions all they can learn. “The the­o­ry holds that Sat­urn long ago had a much more mas­sive ring sys­tem ca­pa­ble of giv­ing birth to larg­er moons,” Mur­ray said. “As the moons formed near the edge, they de­plet­ed the rings and evolved, so the ones that formed ear­li­est are the larg­est and the far­thest out.”

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NASA’s Cassini spacecraft has revealed signs of the formation of a small icy object, possibly a new moon, in Saturn’s rings, astronomers say. The object seems to be tiny and would probably stay that way, about a half mile (about a kilometer) wide, they add. Informally named Peggy, It’s too small to be seen in images so far, but astronomers hope it can provide clues to the formation of Saturn’s known moons. “We have not seen anything like this before,” said Carl Murray of Queen Mary University of London, lead author of a report on the findings. “We may be looking at the act of birth, where this object is just leaving the rings and heading off to be a moon in its own right.” Images taken with Cassini’s narrow angle camera on April 15, 2013, show disturbances at the edge of Saturn’s A ring—the outermost of the planet’s large, bright rings. One of these disturbances is an arc about 20 percent brighter than its surroundings, 750 miles (1,200 kilometers) long and six miles (10 kilometers) wide. The scientists also found unusual protuberances in the usually smooth profile at the ring’s edge. Scientists think the arc and protuberances result from the gravitational pull of a nearby object. The report was published online April 14 in the research journal Icarus. The object isn’t expected to grow larger, and may even be falling apart, astronomers say. But they believe its formation and outward movement could help us understand of how Saturn’s icy moons, including the cloud-wrapped Titan and ocean-holding Enceladus, may have formed in bigger rings long ago. It also offers insight into how Earth and other planets may have formed and migrated away from our star, the sun, they add. Saturn’s icy moons range in size depending on their proximity to the planet: the farther from the planet, the larger. And many of Saturn’s moons consist mainly of ice, as are the particles in Saturn’s rings. Based on these facts, and other indicators, researchers recently proposed that the icy moons formed from ring particles and then moved outward, away from the planet, merging with other moons on the way. “Witnessing the possible birth of a tiny moon is an exciting, unexpected event,” said Cassini Project Scientist Linda Spilker, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. According to Spilker, Cassini’s orbit will move closer to the outer edge of the A ring in late 2016 and provide an opportunity to study Peggy in more detail and perhaps even image it. Moon formation in Saturn’s rings may be ending with Peggy, as the rings now are probably too depleted to make more moons, Murray and his colleagues said. So they’re wringing from the observations all they can learn. “The theory holds that Saturn long ago had a much more massive ring system capable of giving birth to larger moons,” Murray said. “As the moons formed near the edge, they depleted the rings and evolved, so the ones that formed earliest are the largest and the farthest out.”