I'm a postdoc researcher at Lancaster University's Space & Planetary Physics group. Using images from the Hubble Space Telescope and Cassini satellite missions, I study Saturn and its ultraviolet aurora.
Saturn's rings are one of the most recognised and elegant planetary features in our solar system, but the giant, spinning gasmagnet also pulses with ethereal lights and radio emissions from its polar regions. Our eyes would see a pink-purple-red glow because of the Hydrogen atmosphere, unlike Earth's Nitrogen and Oxygen-related red and green arcs. Hubble's cameras are able to see the most intense of Saturn's dancing lights - at far ultraviolet wavelengths - rendered electric blue in visualisations. Saturn's aurora also beat in intensity at the same rate as the planet's rotation. We're only just beginning to understand why.
Hubble took the first photograph of Saturn's aurora in 1997, confirming their existence after glimpses of spectral evidence from the Pioneer and Voyager flybys in the early 1980s. The arrival of the Cassini satellite in 2004 marked a huge step forwards in the exploration of Saturn's magnetic and plasma environment, and its family of moons. The presence of flowing water ice jets from Enceladus has been one of Cassini's most important discoveries. Released particles build up and form an ionised population trapped in the magnetosphere, influencing radio and auroral activity. Cassini's close-up orbits provide a more intimate view of the aurora than Hubble, with finer detail of the shape and brightness of infrared emissions.
An image of Saturn in far ultraviolet from Hubble's Space Telescope Imaging Spectrograph (STIS) instrument. The planet's shadow is cast on the rings in the upper left. Saturn was emerging from a period of equinox in its 29-year orbit of the Sun, when both polar hemispheres were visible from Hubble's orbit around the Earth. The UV emissions associated with the aurora are highlighted in orange. The dark line across the image is a shadow artefact from a support wire on the Hubble satellite. Raw image data from APIS.
Saturn spins extremely quickly (one day lasts under eleven hours) and has a large magnetic field, so rotational processes dominate in the production of aurora.