London, June 10 (ANI): Scientists have finally busted the mystery behind Saturn's midget moons.
Conventional models suggest these moons are so small that collisions with comets should have shattered them much earlier.
But now a group of researchers in France and Britain believe the secret lies in the planet's icy rings.
According to accepted theory, giant planets and their moons slowly accreted out of a gaseous 'protoplanetary disk' around the Sun some 4.5 billion years ago.
But Saturn's baby moons never quite fitted this picture.
At less than 50 kilometres across, comets should have destroyed them over that period.
And over time, moons tend to recede from the planets they orbit, just as our Moon is receding from Earth.
But Saturn's moons are in such a close orbit that they would have had to form virtually inside the giant planet.
About six years ago, the Cassini spacecraft relayed images that hinted at an alternative origin.
Sailing past Saturn's outer rings, it found lumps of ice up to 100 metres across, ten times bigger than the rings' other icy particles.
The discovery led some researchers to recall that the moons and the rings share a composition of the purest ice in the Solar System.
"When you put all this together, you had the strange feeling that something is going on in the rings' outer edge," Nature quoted Sébastien Charnoz, of Paris Diderot University, who was involved in the latest research, as saying.
Charnoz and his colleagues, who are based in Paris and at the University of Cambridge, UK, believed the baby moons formed from smaller lumps of ice sticking together on the outskirts of the main rings.
That process, they thought, might have occurred perhaps just 10 million years ago after which the moons migrated outwards.
To prove it, however, would normally require a numerical model that begins at the Solar System's formation and tracks the moons' every orbit since then - all one trillion of them.
With no computer able to perform such a huge calculation, Charnoz's group created a simplified model of moon dynamics and reduced the ring to one dimension.
Once they had tested it by reproducing our own Moon's formation, they applied it to Saturn.
Their model shows that the main A ring, which is about 120,000 kilometres from Saturn's centre and about 15,000 kilometres wide, feeds material to the empty region just outside.
Here the material can clump together into baby moons. The bigger the moons get, the more Saturn's gravitational 'tidal' forces push them outwards.
The model reveals not only why the biggest moons are farthest out, but also the possible origin of the mysterious F ring, a dusty region outside the A ring in which the baby moons currently reside.
According to Charnoz's group, the moons would have generated the F ring's dust through collisions with each other. (ANI)