Astronomers have discovered that the planet Uranus has a blue ring - only the second found in the Solar System. Like the blue ring of Saturn, it probably owes its existence to an accompanying small moon. Scientists suspect subtle forces acting on dust in the rings allow smaller particles to persist while larger ones are recaptured by the moon. Smaller particles reflect blue light, giving the ring its distinctive colour, the US team reports in Science. All other rings - those around Jupiter, Saturn, Uranus and Neptune - are made up of both large and small particles, making the...