Icarus http://doi.org/rfq (2014)

Credit: © NASA / JPL-CALTECH/UNIV. VIRGINIA

Particles in Saturn's largest and most recently discovered ring — the Phoebe ring — are so diffuse that they are difficult to observe. Spacecraft observations confirm that the particles could have originated from collisions with the nearby satellite, Phoebe.

Saturn's most distal ring is thought to be fed by collisions of micrometeoroids or larger objects with Phoebe or one of the other irregular satellites that make up the planet's outermost moons and travel around it on nonstandard orbits. Daniel Tamayo and colleagues at Cornell University, USA, analysed observations by the Cassini spacecraft of sunlight scattered off the Phoebe ring particles. Combined with previous observations at infrared wavelengths from the Spitzer Space Telescope, the team was able to measure the reflectance of light off the particles and show that the reflectivity of the ring material is consistent with material on the surface of Phoebe.

Material cast off Phoebe during collisions should migrate inwards over time and intersect the orbit of another of Saturn's moons, Iapetus. The ring material might thus coat the leading hemisphere of Iapetus, which could potentially explain the puzzling asymmetry in the colouration of the moon's surface.