NASA's Cassini spacecraft has documented the formation of a small icy object within the rings of Saturn that may be a new moon probably no more than half a mile in diameter.
The findings may provide clues to the formation of the Saturn's known moons and give insight into how Earth and other planets in our solar system may have formed and migrated away from the Sun.
Images taken with Cassini's narrow angle camera on April 15, last year 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 per cent brighter than its surroundings, 1,200 kilometres long and 10 kilometres wide.
Scientists also found unusual protuberances in the usually smooth profile at the ring's edge. They believe the arc and protuberances are caused by the gravitational effects of a nearby object.
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.
"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," said Murray.
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.
Many of Saturn's moons are comprised primarily of ice, as are the particles that form Saturn's rings. Based on these facts, 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, California.
According to Spilker, Cassini's orbit will move closer to the outer edge of the A ring in 2016 and provide 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.
"The theory holds that Saturn long ago had a much more massive ring system capable of giving birth to larger moons," Murray said.
The observations were published in the journal Icarus.
