The 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 Credit: NASA/JPL-Caltech/Space Science
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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.
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, and 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 see in images so far.
Scientists estimate it is probably no more than about a half mile 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
comprised 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.
"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 (JPL) 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.
It is possible the process of moon formation in Saturn's rings has ended with
Peggy, as Saturn's rings now are, in all likelihood, too depleted to make more
moons. Because they may not observe this process again, Murray and his
colleagues are 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."
The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. JPL, a division of the California
Institute of Technology, manages the mission for NASA's Science Mission
Directorate in Washington.
To view an image of the Saturn ring disturbance attributed to the new moon,
visit:
For more information about Cassini, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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