Life, Energy, Dynamics and Dark Matter - Exploring X-rays from the Outer Planets

The outer solar system is truly a place of wonders: spectacular auroral displays, so energetic that they could power Human civilization; moons with global sub-surface water oceans - potentially perfect environments for life; magnetic bubbles ('magnetospheres') that are the largest coherent structures in the solar system; intense radiation belts filled with particles so energetic that they travel at close to the speed of light; iconic glistening rings extending 20 times the diameter of Earth into space to encircle their gaseous hosts. How the cosmos creates these marvels and what processes govern them is at the heart of solar system science and this research.

Historically, NASA and ESA's flagship X-ray observatories, Chandra and XMM-Newton, have been widely used to study the unimaginably energetic or large (black holes, neutron stars or the gas that flows between galaxies). However, X-ray observatories also provide invaluable and under-utilised insights into planetary bodies. My research aims to ensure that we fully utilise the diverse range of X-ray capabilities to study the outer planets.

X-rays fluorescence is a process that produces 'fingerprint' signatures of atomic elements. Consequently, it is excellent for determining what atomic elements something is composed of. On Earth, X-ray fluorescence is used for everything from determining whether a piece of art is fake, to identifying lead in paint, chlorine in food and metals in cosmetics. Through the ERF, I will study X-ray fluorescence from Jupiter's moons Io, Europa, Ganymede and Callisto. This will identify which elements are most common on their icy surfaces, distinguishing between different salts in Europa's ocean to identify what conditions are available there for potential life.

Europa orbits Jupiter within Jupiter's magnetosphere. This vast magnetic cavity around the planet forms through the combination of Jupiter's rapid-rotation, strong magnetic field, and the constant injections of plasma (ionised particles) from the volcanoes on Jupiter's moon, Io. Plasma makes up 99% of the observed Universe. Understanding what processes govern the behaviours of plasmas is therefore critical to understanding the matter we observe across the cosmos. I will use X-ray observations in tandem with measurements by spacecraft in orbit at the planets to study these fundamental plasma processes in several ways:
1. exploring Jupiter's dancing auroral displays to probe the flows of particles and the processes that control them
2. analysing X-ray images of the intense radiation belts to determine how they change over time and what processes trigger these changes
3. calculating the X-ray emissions along the boundary between the magnetospheres of Jupiter, Saturn, Uranus and Neptune and the solar wind, laying foundations to take videos of this boundary, to study the global relationship between each planet and its surrounding space envrionment (the solar wind).

The study of exoplanets has shown that Ice Giants are amongst the most common type of planet in the Universe. However, our local Ice Giants, Uranus and Neptune, are very poorly understood. The rapid flybys of the Voyager spacecraft in the 1980s are the only visit we have ever made to either planet. Without any near-term plans to visit these planets, we have to study them through telescopes at Earth. I will seek to acquire new X-ray observing time for Uranus. This will enable us to explore many of the exciting hints suggested by previous observations, testing for the presence of: sparkling X-ray aurorae, the X-ray glow of the rings and potential fluorescence from the atmosphere.

Through these diverse projects, the research programme will usher in a revolution in the uses of X-ray observations for the outer solar system, founding new research fields and leveraging the X-ray waveband to provide unique insights into the mysterious and wonderous worlds in the outer regions of our solar system.