ASTIlluminating Solar-Planetary Interactions

This project investigates how the Sun affects the space environments of the planets Jupiter and Saturn by studying their aurora. The aurora are nature's light show: dancing displays of light near the planet's northern and southern magnetic poles, caused by charged particles crashing into the atmosphere. Known as the northern and southern lights on Earth, these brilliant emissions have fascinated humans throughout history. The aurora reveals the transfer of energy from the Sun, through the stream of solar particles through the solar system, to the planet's local environment. The aurora also reveals how the planet connects with its moons, such as Io and Ganymede at Jupiter, and Enceladus at Saturn. Now we have the opportunity to study aurora at the outer planets in detail using two new space missions: the Cassini Solstice Mission at Saturn and the Juno mission at Jupiter. These spacecraft will fly low over their planet's polar regions simultaneously taking images of the aurora and measuring their presence in the magnetic field and the charged particles above the atmosphere.

I will study images of the aurora and identify the behaviour of different features. The aurorae typically encircle the poles as narrow arcs. Some arcs rotate with the planet but others move more slowly and it is not clear why or how this can happen. There are also patches of aurora at lower latitudes that seem to be related to clouds of hot, ionised particles in the magnetic bubble enveloping the planet (called the magnetosphere). However, how do these particles become accelerated and travel into the atmosphere? Some of the moons also have an auroral spot in the planet's atmosphere showing where they are connected along the magnetic field lines but the intensity of these spots is variable, perhaps due to changes in the conditions near the moon. Bright auroral flares and arcs have also been identified at higher latitudes, which could be the signature of solar particles directly impacting the atmosphere. Combined with the auroral images I will also use measurements of the magnetic field and particles to see how they are linked in different regions, and how they vary over time.

The unique observations by Cassini and Juno will answer some of these outstanding questions about Sun-planet connections:
- Where are auroral particles accelerated at Saturn and Jupiter and what does this mean for other astrophysical particles?
- How can the conditions at the boundary of the magnetosphere affect such a huge system?
- What causes intense auroral flares and how can they appear over such large regions?
- How can changes near Ganymede, which orbits deep inside Jupiter's magnetosphere, affect the aurora? Does the Ganymede-Jupiter connection represent other systems made up of two magnetised bodies?

This project also has more far-reaching impact. Beyond our solar system, over 1000 planets have been detected. If we want to plan and interpret observations of these planets, we need to learn what auroral emissions represent and how their intensity varies. The best way to do this is to use spacecraft to explore the planets in our solar system and learn as much as we can from them.