Investigating planetary aurora

Auroral emissions are stunning, natural phenomena which have been observed in the skies at high-latitudes for thousands of years. As well as being beautiful, they provide key scientific information on how the outer magnetised environment of the Earth – known as the magnetosphere – is connected and influenced by solar activity. Further away in the solar system, we are now learning about similar emissions which exist in the upper atmospheres of Jupiter and Saturn. Imaging these remote planetary auroral emissions with Earth-based telescopes (e.g. the Hubble Space Telescope) or from orbiting spacecraft (e.g. the NASA/ESA Cassini mission at Saturn) provides a fascinating way of directly observing dynamic activity in the magnetospheres of the outer planets which are otherwise invisible to the naked eye. I will use my Philip Leverhulme Prize fund for post-doctoral researchers to investigate the origins of outer planet aurora through data analysis and modelling work, and to assist with the development of new auroral imaging technology which we will propose for a potential mission to Jupiter (if selected by the European Space Agency) in 2012.

Over the last decade, my research interests have focused on the giant rotating magnetospheres of Jupiter and Saturn, with a particular desire to explore and understand the mechanisms which generate the dynamic auroral emissions in their upper atmospheres. The main auroral oval in Jupiter’s polar ionosphere appears to rotate with the planet, an indication of planetary (rather than solar) control – somewhat different to the case of the Earth. My research contributed to the major new understanding that the main aurora is associated with a large-scale electric current system associated with the transfer of angular momentum from the upper atmosphere of Jupiter to the magnetosphere plasma – a process which is essentially trying to keep the plasma (and magnetic field) spinning as the planet rotates. The magnetosphere plasma originates from the moon Io’s continuous volcanic eruptions, and hence the main aurora is driven internally by the presence of Io.

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Saturn’s dynamic aurora viewed with the Hubble Space Telescope (credit: NASA, ESA, J. Clarke (Boston University), and Z. Levay (STScI)).

More recently, my colleagues and I have studied the first remote Hubble Space Telescope observations of Saturn’s aurora, which we simultaneously compared with magnetic field and particle measurements from the Cassini spacecraft. We discovered the electric current system associated with the aurora at Saturn is located at the outer boundary of the magnetosphere. This indicates a solar-type driving mechanism – more like the situation at the Earth.

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Jupiter’s northern auroral regions imaged by the Hubble Space Telescope (credit: NASA/ESA, John Clarke (University of Michigan)).

Having made substantial progress towards understanding the origins of the aurora at Jupiter and Saturn, my research interests are now developing towards designing the space instrumentation for studying planetary aurora. Current and future involvement in a variety of planetary missions will also provide me with an excellent opportunity to further explore and compare planetary magnetospheres in general, while the parallel technology development will allow us to begin to tread the long path towards sending our own instrumentation on a future mission. To be leading a science team on a future solar-system mission would represent an incredibly exciting opportunity, and for me represents the ultimate career achievement.

Dr Emma Bunce
University of Leicester

Emma was awarded a Philip Leverhulme Prize in 2011; providing £70,000 over 24 months.