MYSTERIES OF THE UNIVERSE WHAT CAUSES THE SPOKES IN SATURN'S RINGS?

Smudges around the gas giant have begun to appear again. Scientists have plenty of time to study them, but will they finally work out what's happening?

- David Crookes

From a casual perspective, Saturn's iconic rings look almost perfect. Made up of billions of particles of ice and rock, which are thought to have come from comets, asteroids or shattered icy moons, they appear to seamlessly encircle the gas giant like a huge vinyl record. Since they were discovered by Galileo in 1610, the rings have become an immense source of fascination for astronomers, with so many discoveries having been made about them since. A lot of our knowledge of the rings came from the Voyager mission in the early 1980s, which gave us the first close-up images of the planet's complex system.

As Voyager 1 got within 50 million kilometres (30 million miles) of Saturn on 6 October 1980, it allowed astronomers to see some unusual marks. Rather than venturing in the same direction as the rings, they appeared to cut across them, like rods radiating from the centre of a wheel. Scientists had never seen this before, and they were intrigued to discover what may have been causing them. Named 'spokes' they've caught the imagination of researchers ever since. "The spokes are fascinating because they were so unexpected when Voyager flew by - we expected pristine icy and maybe rocky pieces, but didn't expect to see these ethereal dusty features," Dr Amy Simon, head of the Hubble Outer Planet Atmospheres Legacy (OPAL) program, tells All About Space. Yet there they were in all their glory, viewable again when Voyager 2 was within 4 million kilometres (2.5 million miles) of Saturn on 22 August 1981. And so a mystery was born.