Solar System Physics PhD Projects

The following are typical PhD projects offered in Solar System Physics. Specific projects may vary from year to year, and related projects may be offered in consultation with the institute.

For further information please contact us at imaps@aber.ac.uk

3D structure of the solar wind

Supervisor: Dr Andy Breen

The solar wind is the extended solar atmosphere, expanding into space at supersonic speeds. The outflowing plasma is not of uniform density, and if a compact astronomical radio source (such as a quasar) is observed when it lies close to the Sun in the sky then its brightness varies on timescales of 0.1-10s, as drifting density irregularities in the solar wind cast a moving diffraction pattern across the Earth. By sampling this diffraction pattern with two widely-spaced radio telescopes we can determine the outflow speed of the solar wind at distances of 5-100 solar radii - a region which is inaccessible to other techniques. We use measurements from the EISCAT facility in arctic Scandinavia and the MERLIN array of radio telescopes in the UK, in conjunction with co-ordinated measurements from optical instruments on the SoHO and (from early 2007) STEREO spacecraft to study the evolution of the large-scale 3D structure of the solar wind, together with the development and propagation of coronal mass ejections and the large-scale direction of the solar magnetic field. Advanced data visualisation techniques will be used to combine the datasets. This project will involve extensive collaborations with experimenters and theorists worldwide, and a willingness to travel to the high arctic and to the USA or Japan is essential.

 

Solar wind acceleration

Supervisors: Dr Andy Breen and Dr Xing Li

The solar wind is the supersonically expanding extension into space of the solar atmosphere and is known to be accelerated as it emerges from the Sun's corona. Research at Aberystwyth and elsewhere has established that heavy ions in the solar wind are accelerated more rapidly, and recently evidence has emerged that small-scale turbulent structures are boosted in speed above the background flow. This project combines Aberystwyth's expertise in radio scintillation studies of the solar wind, which is unique in Europe, with computational modelling of solar wind acceleration. Students taking on this project may be required to travel to the high arctic to make observations and to the USA to engage in collaborative work with other modellers.

Disturbances in the solar system

Supervisors: Dr Andy Breen and Professor Manuel Grande

Solar eruptive events - flares and coronal mass ejections (CMEs) - are the most energetic events in the solar system and can have significant effects on Earth, disrupting communications and giving rise to aurora. The path of the CME though interplanetary space is influenced by its interaction with the background solar wind. This project combines measurements from the NASA STEREO spacecraft (due for launch in autumn 2007) with radio observations from EISCAT and MERLIN to study CME/solar wind interaction. Measurements made by instruments on planetary-orbiting spacecraft (Mars Express and Venus Express) will be used to investigate solar wind and CME effects on planetary environments, and the results compared with terrestrial observations and model results in collaboration with other members of the solar system physics group.

Global Maps of Lunar Elemental Abundances

Supervisor: Professor Manuel Grande

 

The C1XS X-ray spectrometer on the Indian Chandrayaan Lunar Mission, due to launch in spring 2008 will provide a hitherto unavailable set of measurements of the surface abundances of Lunar rock forming elements. Aberystwyth as PI institute will play a leading role in data analysis. The first requirement is for global maps. These will form the basis of all subsequent scientific analysis. Key questions involve the distribution of Magnesium as a diagnostic of Lunar magma ocean formation, and the investigation of impact basin floor composition as a probe of deeper Lunar composition. The potential for remote sensing of other constituents such as Sodium and Aluminium can also open new areas. It is envisaged that a studentship dedicated to work on production and interpretation of these maps will provide a unique training and for a basis for a career both in space exploration and in Lunar and Planetary science, both areas where the UK offers expanding prospects.

Oxygen and Helium in the Terrestrial Magnetosphere

Supervisor: Professor Manuel Grande

The plasmasphere is the cold (~1eV), ionised region of the upper atmosphere. It co-rotates with the Earth on the closed magnetic field, but is strongly coupled to the solar wind as well as the ionosphere. Its physical parameters (such as size, shape, density distribution, temperature, etc.) are subject to solar effects, via electromagnetic storms and substorms. During enhanced magnetic activity, the size of the plasmasphere reduces significantly, as the outer flux tubes are eroded away to the dayside merging region. After the activity subsides, refilling of depleted flux tubes via the ionosphere, of which the upper extension at mid and low latitudes is the plasmasphere, leads to an increase of the plasmaspheric size.

This project will investigate the sources and sinks of energetic particles in the terrestrial magnetosphere, particularly in the tail, ring current and radiation belts, and cusp, using data from Cluster, Polar CRRES and DoubleStar, augmenting in situ composition measurements with remote sensing measurements using IMAGE.

There is still much work to be done in unravelling the stormtime composition history, and how it persists and is modified in quiet times. In fact, the life-cycle of oxygen and helium in the terrestrial magnetosphere has never been fully explained. Helium enters the magnetosphere either singly charged from the ionosphere, possibly via plasmasphere refilling and subsequent erosion and energisation, or doubly charged from the solar wind, while charge exchange from double to single can take place for stably trapped ions. This project will follow on from current work to produce a global picture of oxygen and helium dynamics in storm and quiet times for different parts of the solar cycle.

Modelling of planetary magnetospheres, ionspheres and atmospheric erosion at Venus and Mars

Supervisors: Professor Manuel Grande, Dr Balazs Pinter and Dr S. Eleri Pryse

The Earth's atmosphere is a complex system which has undergone a great deal of study and modelling. Recently, efforts have been made to apply this understanding of the Earth's atmosphere to that of other planets. The Venusian atmosphere is unmagnetised and without the magnetospheric cavity to shield the upper atmosphere from the oncoming solar wind, Venus will be subject to comet-like atmosphere erosion processes and solar-wind-induced current systems, which have no terrestrial counterparts.

At Venus, where erosion processes should be highly efficient, we see an extremely dense atmosphere. This is suggestive of refilling of the atmosphere by, for example, volcanism. However there is no evidence as to whether such processes are still active, or the legacy of past episodes.

This project will compare the atmospheres of Earth and Venus by developing existing Earth atmosphere models for use in the Venusian case. The modelling will be strengthened by probing the interaction between Venus and the solar wind using instruments on the Venus Express probe.  There is scope to expand the project to include the atmosphere of Mars in the comparison.

Coronal Heating and Solar Wind Study

Supervisor: Dr Xing Li

The temperature of our solar atmosphere increases from a level about 6000K at photosphere (where our visible light comes from) to about a million K at the dilute corona. The mechanisms responsible for this enormous heating have puzzled solar physicists for decades.

The expansion of the corona into interplanetary space along open magnetic field lines produces the solar wind. However, the acceleration of the wind poses physicists another challenge. Classical solar wind theory cannot account for the properties of the solar wind observed by space probes. It is now understood that the coronal heating and solar wind acceleration may be the two aspects of a single problem. Hence they must be treated on an equal footing.

Observational and theoretical progresses in the past decade concluded that the acceleration of the solar wind primarily occurs in the first few solar radii where coronal heating is continuously going on. However, our knowledge of the gas properties in the first solar radii is still limited. We use SoHO EUV observations to probe the property of the gases in the first few solar radii and our state-of-the-art solar wind models to understand the physical processes.

The grand goal of the project is to understand the coupling of energy and mass between the solar photosphere and the solar wind by combining observations and numerical modelling. A critical issue of the solar wind study will be to develop diagnostic tools to derive solar wind outflow speeds using a Doppler Dimming technique. Such a technique when the Sun is at a minimum phase of activity has already been successfully developed. Doppler dimming technique still requires significant improvements when the solar activity is strong. Our multi-dimensional and multi-component solar wind codes will be used to study the global evolution of the solar wind.

Plasma transport processes in Coronal Mass Ejections (CMEs)

Supervisors: Dr Xing Li and Dr Andy Breen

To understand the physics of CMEs, researchers traditionally model CMEs using the framework of single fluid MHD theory. In this theory, the energy equation is dramatically simplified by adopting a polytropic equation with a small polytropic index. The detailed energy release process which may be the key for understanding the physics of CMEs is largely ignored under such theory. Indeed, observations have shown that the energy release in CMEs is an ongoing process. Oxygen ions have been observed to be heated to hundreds of millions of degrees in CMEs. CMEs have complex magnetic structure and strong current sheets, and plasma waves and turbulence are likely to be important in the current sheets.

The aim of this project is to model CMEs using a multi-fluid approach. Multi-fluid models are essential to describe the evolution of the solar wind properly, since different species have distinct properties. Currently no such 3D model exists. This project will extend our multi-fluid 2.5D solar wind code to 3D, and use this to study the global impact of transient events (such as solar flares and local magnetic reconnections in active regions). This approach will shed light on the role of MHD waves/turbulence in the energy release of CMEs since plasma waves and turbulence may impact different particles in a dramatically different way.

Resonant coupling of helioseismic modes into the solar atmosphere

Supervisor: Dr Balazs Pinter

The global solar photospheric oscillations (e.g., the fundamental f- and pressure p-modes with power peaks at around the period of 5 minutes) have proved to be an excellent diagnostic tool for revealing the subtleties of the structure and physical processes of the solar interior. Observations show that the f- and p-modes, which are often referred to as cavity modes, are not completely trapped in the solar interior and can leak into the atmosphere. Hence, observed f- and p-mode oscillations can also provide a novel diagnostic to probe the complex magnetic structure and dynamics of the solar atmosphere. This project will develop a new method of using the solar global oscillations in atmospheric diagnostics by modelling the coupling of the solar interior to the lower and outer solar corona. In particular, questions to be addressed are:

• How deeply do the f- and p-mode oscillations penetrate into the atmosphere?
• How efficient is the coupling of the atmospheric magnetic fields to global f- and p-modes?
• How can observations of solar global modes be used to probe the physics of the solar atmosphere?

The answers to these questions will considerably improve our current understanding of how the apparently distinct layers of the Sun are organically coupled together into one major physical system. New observational techniques, resulting from these theoretical models, will be developed and implemented for local coronal seismology and for the search and analysis of waves and oscillations in various regions of the Sun, from sunspots, through solar tornadoes to solar wind.

Small Scale Erosional and Depositional Lunar Surface Processes

Supervisor: Dr Anthony Cook and Professor Manuel Grande

Crater count measurements of the lunar surface imply that the geology is of the order of hundreds to thousands of million years old. However effects have been observed that suggest that there are at local scales minor changes. The first of these are from impacts from kg order mass meteorites that have been detected in the past by Apollo seismometers, and more recently by confirmed observations of impact flashes as seen through Earth-based telescopes. The second surface process observed is the electrostatic charging and subsequent levitation of dust particles as detected from the Apollo LEAM instrument and also from dust clouds horizon glow probably seen from orbit by the Clementine spacecraft and Apollo astronauts. Thirdly it has been speculated that interior trapped gases, including Radon and Argon leak out of the Moon’s surface, occasionally in the form of sudden pressurized releases – the Ina formation is one candidate site of past eruptive out-gassing. The proposed project can be tackled in either of two ways. Firstly a practical approach that would look for evidence of localized changes over the Moon’s entire surface of 38 million square kilometres by comparing automatically 1960/70’s era high resolution spacecraft photographs with modern era Lunar Reconnaissance (LRO). In order to reduce the search space areas will be targeted for which the locality of impact flash events are known, where surface maturity maps suggest a freshly disturbed soil, and where unusual surface features have been identified using results from a citizen science internet tool called MoonZoo. The second possible approach to the PhD is to construct theoretical models of how dust particles can become charged and levitate above the lunar surface; current models do not explain this phenomenon fully, especially how dust particles can attain altitudes of the order of 100km. The model should include the shielding effects of topography, the solar wind, and passages through the Earth’s magnetotail. The relevance of this PhD to modern space exploration is that it could help to identify and catalogue interesting targets for future surface missions, and predict which parts of the Moon could prove a dust hazard for astronauts and rovers.

Theory and Applications of a New MHD Instability

Supervisor: Dr Youra Taroyan

Many physical processes in nature are governed by macroscopic instabilities. Well-known examples are the Rayleigh-Taylor (heavy fluid overlying a light fluid) and the Kelvin-Helmholtz (wind blowing over water) instabilities: small perturbations grow leading to large scale changes in the physical system and transfer of energy. The presence of a magnetic field embedded in a fluid introduces new types of perturbations which may also grow.

The proposed project is dedicated to the theory and applications of a new magneto-hydrodynamic (MHD) instability. The energy extracted from a compressible flow leads to the amplification of arbitrary Alfvenic disturbances. The Alfven instability does not require high flow speeds or shear and is therefore expected to play an important role in magnetic structures of the lower solar atmosphere where upflows and associated nonthermal broadenings are commonly observed with different instruments such as SoHO/SUMER and Hinode/EIS.

The first part of the project is concerned with developing the linear theory of the Alfven instability in magnetic flux tubes: the effects of atmospheric stratification and expansion, the threshold speeds, the spatiotemporal behaviour of the amplified disturbances will be investigated semi-analytically in the linear regime. In the second part, numerical examination of the nonlinear evolution of the instability will be carried out: the energetic and dynamical consequences will be investigated. The amount of energy extracted from the flow and dissipated through the amplification process will be estimated for typical conditions on the Sun. The role of the instability mechanism in solar/stellar coronal heating and wind acceleration will be addressed.