Spotlight on Saturn's Aurorae

A UK team of researchers have discovered a secondary aurora sparkling on Saturn and also started to unravel the mechanisms that drive the process. Their results show that Saturn’s secondary aurora is much more like Jupiter’s in origin than it is the Earth’s.

Aurorae are caused when charged particles stream along the magnetic field of a planet and into its atmosphere. On Earth these charged particles come from the solar wind – a stream of particles that emanates from the Sun. Variations in the Sun control the frequency and intensity of these beautiful displays that can also herald problems – such as interference with satellite communications and power distribution.

On Jupiter however, the dominant source of particles is its own moons, particularly Io which throws out roughly one tonne of volcanic material every second. Bombarded by sizzling radiation, some of this material is broken down into plasma - a mixture of positive and negative electrically charged particles - and is pulled in Jupiter’s magnetic field. It co-rotates in a sheet of plasma around the planet, but as the particles spread out the magnetic field weakens and this breaks down causing the particles to crash into Jupiter’s atmosphere creating an aurora.

On Saturn, whilst one aurora had been observed, the primary source of the particles was unclear. Tom Stallard of the University of Leicester explains “At Saturn, scientists were unsure whether the aurora was caused by the solar wind or by particles from its own system. When we discovered the second zone of aurorae on Saturn, we realised this aurora, unlike the one already seen on Saturn, was behaving in the same way as Jupiter’s, largely unaffected by the solar wind, dominated by the rotation of the planet.”

Modelling the aurorae on Jupiter and Saturn shows that both exhibit aurora in the positions where the co-rotation between the planet and its plasma sheet breaks down.

Stan Cowley of the University of Leicester said, “We can now say that some of Saturn’s aurorae are like Jupiter’s and they have a common formation process. Further, our discovery of the secondary aurora on Saturn suggests that we shall also find one on Jupiter within its polar region.”

As well as the measurements from NASA’s InfraRed Telescope Facility in Hawaii used in this research, Saturn’s main aurora has been studied using the Hubble Space Telescope operated by NASA and ESA.

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