Astronomy

Aurora is 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 communication’s satellite 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. Some of this becomes ionised (plasma) and is pulled in Jupiter’s magnetic field. It co-rotates in a plasma sheet 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. At Saturn, scientists were unsure whether the aurora was caused by the solar wind or by particles from its own system.

Recently, a team from University of Leicester, UK, 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. The 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. The source of Saturn second aurora is thought to be its moon, Enceladus, which sloughs off an estimated 100 kilograms of material per second into orbit around Saturn via plumes of water vapor first discovered in 2005.

Pictured here is the Saturn’s main auroras, imaged by the Hubble Space Telescope. It is thought to be caused by the solar wind. Saturn’s secondary auroral ring, however, is too faint to see. To spot it, astronomers used a ground-based NASA’s InfraRed Telescope Facility to look at infrared light near Saturn’s south pole.

The results has been published in June 19th issue of scientific journal Nature on a paper titled “Jovian-like aurorae on Saturn” by Tom Stallard et al. (Image credits: J Trauger/NASA)

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