NASA Cassini Images May Reveal Birth of a Saturn Moon

NASA’s Cassini spacecraft has documented the formation of a small icy object within the rings of Saturn that may be a new moon, and may also provide clues to the formation of the planet’s known moons.

The disturbance visible at the outer edge of Saturn's A ring in this Cassini image could be caused by an object replaying the birth process of icy moons.

The disturbance visible at the outer edge of Saturn’s A ring in this Cassini image could be caused by an object replaying the birth process of icy moons.

Images taken with Cassini’s narrow angle camera on April 15, 2013, show disturbances at the very 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 6 miles (10 kilometers) wide. Scientists also found unusual protuberances in the usually smooth profile at the ring’s edge. Scientists believe the arc and protuberances are caused by the gravitational effects of a nearby object. Details of the observations were published online today (April 14, 2014) by the journal Icarus.

The object is not expected to grow any larger, and may even be falling apart. But the process of its formation and outward movement aids in our understanding of how Saturn’s icy moons, including the cloud-wrapped Titan and ocean-holding Enceladus, may have formed in more massive rings long ago. It also provides insight into how Earth and other planets in our solar system may have formed and migrated away from our star, the sun.

“We have not seen anything like this before,” said Carl Murray of Queen Mary University of London, the report’s lead author. “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.”

The object, informally named Peggy, is too small to be seen in images so far. Scientists estimate it is probably no more than about a half mile (about a kilometer) in diameter. 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 are composed primarily of ice, as are the particles that form 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.

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