Plasma-neutrals interactions at Saturn

We will use spacecraft and telescope measurements to explore Saturn's space environment. We will look at the cloud of material coming from Saturn's icy moons and rings and how this can stop charged particles that are trying to move along Saturn's magnetic field. We will measure the solar wind surrounding Saturn's magnetic bubble, and the aurora emitted from the planet's poles, to understand what's driving the changes in the neutral cloud and the charged particles. We will also study particles found close to the planet, to work out where they have come from.

Saturn's magnetosphere is fundamentally different from Earth's because it hosts a cryovolcanic moon, Enceladus, that orbits close to the planet. Outgassing from fissures on Enceladus's icy surface releases significant amounts of water into the surrounding space environment. These neutral particles play a vital role in governing the dynamics of a planetary magnetosphere both as a potential source of plasma and a sink of energetic ions. These molecules spread out to form a torus around Enceladus's orbit. Some particles are ionised to produce the water group ions which populate Saturn's magnetosphere, but overall Saturn's magnetosphere is uniquely dominated by neutrals.

This project investigates how the flow of energetic plasma in the magnetosphere interacts with the vast clouds of water neutrals around Saturn. Energetic Neutral Atoms (ENA) are created when energetic ions collide with neutrals and observing ENA provides a useful picture of plasma flows. A balance of inward and outward flow is maintained over time, but during dynamic events such as magnetotail reconnection, fast flows deliver energetic plasma close to the planet, when we can observe characteristic responses in the auroras, particles and magnetic fields. Volcanic activity on Enceladus is also known to vary in time, and we will also consider how this variation in plume outgassing drives asymmetries in the neutral cloud, and how global plasma flows might ultimately be driven and amplified by small-scale, inner magnetosphere dynamics.

We will also investigate ENA emissions from Saturn's atmosphere to diagnose the origin of the driving energetic ions and their often-pulsed behaviour. Finally, we will track injections of energetic plasma into the inner magnetosphere to verify the role of charge exchange as a sink for different particle energies at decreasing radial distances.