They look more like flying-saucers than icy moons, but Pan and Atlas are two of Saturn's strangest satellites. Scientists have long been puzzled by how the oddly-shaped moons, which are only 20miles across, came to be.
Researchers based at the European Space Agency now think they have some answers after studying several years worth of cosmic images. They realised that 14 of Saturn's small moons had a very low density - about half that of water ice - and shapes that suggested they had grown out of the rings themselves.
However, they would have needed a jump start as it is not gravitationally possible for small particles to fuse together within the rings. Therefore, each moon would have started with a massive core that was a leftover from the original collisions that caused the rings.
Carolyn Porco from ESA, said: 'We think the only way these moons could have reached the sizes they are now, in the ring environment as we now know it to be, was to start off with a massive core to which the smaller, more porous ring particles could easily become bound.'
By this process, a moon will grow even if it is relatively close to Saturn. The result is a ring-region moon about two to three times the size of its dense ice core, covered with a thick shell of porous, icy ring material.
Simulations performed at Southwest Research Institute in 2010 suggest that Saturn originally had several large Titan-sized moons, which spiraled into the planet during its early history. As the final lost satellite neared Saturn, heating caused by the flexing of its shape and the planet's gravity would cause its ice to melt and rock sink to its centre.
Planetary tidal forces as it crossed the region of the current B ring would then have stripped material from its outer layers, creating the initial ice ring. Dr Robin Canup from the SwRI Planetary Science Directorate in Boulder, who led the study, said: 'The new model proposes that the rings are primordial, formed from the same events that left Titan as Saturn's sole large satellite,.
'The implication is that the rings and the Saturnian moons interior to and including Tethys share a coupled origin, and are the last remnants of a lost companion satellite to Titan.'
But how then to explain the strange ridges that give Pan and Atlas their unique shapes?
The answer, scientists suspect, lies in accretion discs, that are seen at all scales in the universe from planetary rings to galaxies. Essentially as the disc spins, forces cause the edges of the structure to flatten out and a bulge to form towards the centre.
'Our computer simulations show that the ridges must have accreted rapidly when Saturn's rings were thin, forming small accretion disks around the equators of Pan and Atlas,' said Sebastien Charnoz, from the University Paris-Diderot in France.