A previously unknown planetary ring, the largest discovered in the solar system, has been found around Saturn. The circle of dust, about 50 times farther out than the planet’s other rings, is believed to be debris from one of Saturn’s moons, Phoebe.
The ring describes the outer boundaries of Phoebe’s orbit, and is at an angle of 27 degrees relative to Saturn’s inner rings. Like Phoebe, the ring orbits in the opposite direction to all of Saturn’s other large moons.
The discovery is reported in a study published today in the journal Nature, which says that the dust comes from minor impacts on Phoebe. The dust does not remain in the ring’s orbit indefinitely but slowly gravitates towards Saturn, some of it being deposited on nearby moons on the way.
The dusty hoop extends about 13 million kilometres — or eight million miles — from the planet, and would appear to be twice the size of the full Moon if it were visible from Earth.
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