to the orbit of Phoebe was reported. The disk was aligned edge-on to Earth at the time of discovery. This disk can be loosely described as another ring. Although very large (as seen from Earth, the apparent size of two full moons), the ring is virtually invisible. It was discovered using NASA's infrared Spitzer Space Telescope, and was seen over the entire range of the observations, which extended from 128 to 207 times the radius of Saturn, with calculations indicating that it may extend outward up to 300 Saturn radii and inward to the orbit of Iapetus at 59 Saturn radii. The ring was subsequently studied using the WISE, Herschel and Cassini spacecraft; WISE observations show that it extends from at least between 50 and 100 to 270 Saturn radii (the inner edge is lost in the planet's glare). Data obtained with WISE indicate the ring particles are small; those with radii greater than 10 cm comprise 10% or less of the cross-sectional area. Phoebe orbits the planet at a distance ranging from 180 to 250 radii. The ring has a thickness of about 40 radii. Because the ring's particles are presumed to have originated from impacts (micrometeoroid and larger) on Phoebe, they should share its retrograde orbit, which is opposite to the orbital motion of the next inner moon, Iapetus. This ring lies in the plane of Saturn's orbit, or roughly the ecliptic, and thus is tilted 27 degrees from Saturn's equatorial plane and the other rings. Phoebe is inclined by 5° with respect to Saturn's orbit plane (often written as 175°, due to Phoebe's retrograde orbital motion), and its resulting vertical excursions above and below the ring plane agree closely with the ring's observed thickness of 40 Saturn radii. The existence of the ring was proposed in the 1970s by Steven Soter. The discovery was made by Anne J. Verbiscer and Michael F. Skrutskie (of the University of Virginia) and Douglas P. Hamilton (of the University of Maryland, College Park). The three had studied together at Cornell University as graduate students. Ring material migrates inward due to reemission of solar radiation, with a speed inversely proportional to particle size; a 3 cm particle would migrate from the vicinity of Phoebe to that of Iapetus over the age of the Solar System. The material would thus strike the leading hemisphere of Iapetus. Infall of this material causes a slight