UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS

High resolution X-ray spectroscopy of Active Galactic Nuclei

Prof. Graziella Branduardi-Raymont

High resolution X-ray spectroscopy is one of MSSL's astrophysics group well established lines of research, focussing on the study of Active Galactic Nuclei (AGN), and the ionised gas (the 'warm absorber') that lies in our line of sight to the central engine. The detailed analysis of the absorption features imprinted by the gas on the nuclear X-ray continuum, as well as of the emission lines generated in the gas, is a powerful diagnostic of the physical conditions of the environment surrounding the nuclear black hole, of the dynamics of the gas, its chemical composition and ionisation state. The gas is generally observed to be outflowing from the innermost regions of the AGN; the outflow rates are often comparable to, or even larger than, those of the matter accreting onto the black hole, and leading to the AGN powerful X-ray emission. This suggests that both outflow and accretion play a major role in the evolution of the black hole mass and of the AGN as a whole. The feedback mechanism associated with this may regulate star formation in the host galaxy, and may determine the known relationship between the mass of the black hole and that of the surrounding spheroid. The research student is expected to become very familiar with AGN science and learn the techniques employed in the analysis of high-resolution X-ray spectra, with the aim to contribute to and to further our investigations in the topics outlined above. The student will employ archive as well as guest observer data obtained with the XMM-Newton Reflection Grating Spectrometer (RGS), which MSSL contributed to build. The knowledge acquired in building, testing and calibrating the instrument has translated into a deep understanding and interest in the exploitation of the data returned by the spectrometer. This combination of knowledge and observational expertise in high resolution X-ray spectroscopy is unique among UK astronomy groups, and puts us in a strong position for exploiting high-resolution data from the non-dispersive X-ray spectrometers of the future.

RGS spectrum of the Seyfert 1 galaxy NGC3516,fitted using the 'slab' absorption model. Some of the strongest absorption features are labelled (from Mehdipour et al. 2010, A&A, 514,100 - Missagh Mehdipour is a current MSSL PhD student).

Artist's impression of the core of the Narrow Line Seyfert 1 galaxy Arakelian 564 showing the limits (set by the RGS data) on the locations of the broad emission, narrow emission and absorption line regions (from Smith et al. 2008, A&A, 490, 103 – Rebecca Smith was a PhD student at MSSL who received her doctorate in 2009).

X-ray studies of planets in our solar system

Prof. Graziella Branduardi-Raymont

Over the last decade the Chandra and XMM-Newton observatories have revealed the beauty and multiplicity of X-ray emissions from the planets in our solar system. This research field encompasses planetary physics, solar science and the response of solar system objects under the effects of the Sun’s activity. 

Jupiter's polar regions show bright soft X-ray aurorae, with a line-rich spectrum arising from the charge exchange interactions of atmospheric neutrals with local and/or solar wind high charge-state heavy ions, accelerated in the planet’s powerful magnetic environment. At energies above ~3 keV the X-ray spectrum of the Jovian aurora becomes featureless, pointing to an origin from electron bremsstrahlung. Jupiter’s atmosphere also scatters solar X-rays, so that at low latitudes the planet's disk displays an X-ray spectrum that closely resembles that of solar flares. 

Saturn has not revealed X-ray aurorae (yet), but its disk X-ray brightness, like Jupiter’s, strictly correlates with the Sun's X-ray output, pointing again to scattering of solar X-rays. Remarkably, we see X-rays from Saturn's rings as well, generally from bright spots localised on their East ansa. 

Mars and Venus lack a strong magnetic field, yet they both show X-ray emissions from their disks and exospheres: here solar X-ray scattering and charge exchange (by solar wind ions with the exosphere neutrals) are thought to be at work, respectively; the two spectral components have been clearly separated at high spectral and spatial resolution. 

Finally, the Earth's X-ray aurorae, like those in visible light, show a high degree of variability in intensity and morphology, both at soft and hard X-ray energies. And solar wind charge exchange in the Earth’s exosphere has been directly revealed by XMM-Newton along lines of sight crossing the terrestrial magnetosphere.

In summary, we have come to realise that planetary X-ray emissions are powerful probes of the conditions of the solar wind and of the planetary response to solar activity, and that their study provides novel insights about the close relationships between planets and their parent star.

The PhD project is envisaged to be based on the investigation of Jupiter, through the analysis of Chandra and XMM-Newton data. 

X-ray spectral maps (energy increasing from left to right and from top to bottom) of Jupiter obtained from XMM-Newton observations. The morphology of the planet is clearly different at different energies: the aurorae are bright at soft (charge exchange) and hard energies (bremsstrahlung) while the disk emission (scattered solar X-rays) disappears above ~3 keV.

High-resolution Cosmological Simulations of Disc Galaxies

Dr. Daisuke Kawata

 ESA's next cornerstone mission, Gaia, will uncover revolutionary detailed views of the Milky Way. In addition, the large scale survey, like Euclid, will provide us the snapshots of the formation history of the disc galaxies, like the Milky Way. Computer simulation of galaxy formation is a powerful tool to connect these snapshots information, and help us to understand the physical process of galaxy formation and evolution. The objective of this project is to improve and optimise the MSSL's original particle-based galactic chemodynamics code, GCD+, on the state-of-the art supercomputers in the UK and Europe, and run unprecedentedly high-resolution numerical simulations of the disc galaxy formation to compare with the future observations and study the galaxy formation.

We seek a student who like computer programming and enthusiastic enough to tackle the challenging project.

Above: Snapshots from a cosmological simulations with GCD+. Dark matter density map of a portion of the cosmological simulation volume (upper panels), and predicted B-band image of the simulated disc galaxy (lower panels). 

Measuring Dark Energy Properties with 3D Weak Lensing

Dr T Kitching

We face a turning point in our understanding of the Universe. It is now known that it consists of two components named, to partly reflect our ignorance of them, dark matter and dark energy. Dark matter accounts for approximately 20% of the content of the Universe, so called because it does not emit or absorb light, it is thought to be a new type of particle beyond the standard model of particle physics. Much more mysterious though is dark energy, a phenomenon that is causing the expansion rate of the Universe to accelerate. The presence of dark energy could be explained by a “vacuum energy” however the density of dark energy inferred from current observations is 1060 times larger than that expected from particle physics, this is the largest discrepancy between theory and observation ever encountered in physics, a factor which cannot be reconciled without a fundamental re-evaluation of our understanding of physics. 

To address the most important questions in cosmology requires the best and most comprehensive data analysis methods. Gravitational lensing, the effect whereby photons are deflected from a straight-line path by the presence of a massive object distorting spacetime locally, is widely accepted to be such a method. This phenomenon, predicted by Einstein, led to the acceptance of General Relativity as our canonical theory gravity in 1919. Now, almost 100 years after this discovery this same phenomenon applied to the lensing of light by large-scale structures of the Universe, as a function of distance or look-back time, enables us to map the 3D dark matter structure of the Universe as well as its expansion history. This combination of lensing information and distance is known as 3D weak lensing this PhD project will build on this foundation, and apply the best analysis methods to the best data available. 

Development of 3D weak lensing is required for several reasons 1) new theoretical models need to be included, in particular parameterizations of modifications of gravity that extend General relativity to include a potential mechanism to explain dark energy 2) systematic effects, in particular those caused by the alignment of galaxies, that can mimic the weak lensing signal, need to be included. Without these improvements 3D weak lensing cannot reach its full potential. 

This PhD will apply these new developments the state-of-the-art gravitational lensing data sets: the 154 square degree CFHTLenS survey which is already available and the 1500 square degree ESO KiDS survey that is observing data now. In addition 3D weak lensing–CMB cross correlation statistics will be investigated with an aim to apply this to KiDS and Planck. Finally, this project will build the analysis tools expected to be used in the upcoming ESA Euclid mission in which MSSL has a leading role. In order to ensure a successful PhD this project contains theoretical, simulation and data analysis elements that are flexible such that they can fit with the students skills and expertise.  

Left: (copyright Columbi & Mellier) the large-scale cosmic web distorts the image of background galaxies in a measurable way that can help in determining the nature of dark energy. 

Right: (copyright NASA) the Hubble Space Telescope Ultra Deep Field, the Euclid ESA mission will observe tens of thousands times more data with a similar fidelity with an objective to use gravitational lensing to determine dark matter and dark energy properties.

Measuring the Geometry of the Universe with Clusters of Galaxies

Dr T Kitching 

Determining the geometry of the Universe is an important test of the standard cosmological model; that contains to unknown components, dark energy and dark matter, that account for 96% of the mass-energy budget but whose nature is entirely unknown. Dark energy is the phenomenon causing a change in the rate of expansion (an acceleration), hence any method that probes the rate of change cosmic environment or the expansion history will be sensitive to the exact nature of dark energy. 

When galaxies are observed behind galaxy clusters we see their light distorted by the warping of spacetime caused by the mass of the cluster, an effect known as gravitational lensing. The amount of distortion depends on properties of the cluster and also on the geometry of the Universe. This PhD will develop a well-understood method that takes ratios of the gravitational lensing signal, which can remove the contaminating effects of the details of the cluster to isolate the signal cause by the geometry of the Universe. 

One of the objectives of this PhD will be to develop these methods to the point that they will be able to test many competing theories for dark energy. As an example one such explanation is that gravity deviates from General Relativity on large scales – if the gravitational force becomes weaker or even repulsive on cosmic scales this could cause an accelerating expansion. 

This PhD will apply these new developments to the state-of-the-art gravitational lensing data sets: the 154 square degree CFHTLenS survey which is already available and to galaxy clusters observed using the Hubble Space Telescope, and also to the 1500 square degree ESO KiDS survey that is observing data now. Finally, this project will build the analysis tools expected to be used in the upcoming ESA Euclid mission in which MSSL has a leading role. In order to ensure a successful PhD this project contains theoretical, simulation and data analysis elements that are flexible such that they can fit with the students skills and expertise.  

Above: A massive galaxy cluster Abell 1689 (copyright NASA), the gravitational lensing effect caused by the warping of spacetime by the clusters mass, can be seen as highly distorted arcs but in fact every galaxy in the image is at least weakly distorted and this distortion depends on the geometry of the Universe.

Explaining cause and spectra of X-ray bursts from magnetars

Dr. Silvia Zane

On the observational ground, the most distinctive properties of magnetars is the emission of short, intense bursts of hard X-rays/soft gamma-rays.  In the magnetar scenario bursts are believed to originate from a hot, magnetically-confined pair plasma (a "fireball") which forms above the star surface because of the huge energy injected in the magnetosphere as a consequence of a crustal displacement (a "starquake").

During 2006 we observed, with the  Swift X-ray satellite an intense burst `"forest" from SGR 1900+14 which lasted for ~30 s, during which 7 intermediate flares (IFs) were detected. These events have properties in between those of normal bursts and giant flares, i.e. ~1 s duration and luminosity up to ~ 1E42 erg/s. This unique data set provided us with the most complete information to date on SGR bursts. Data were well represented by a two-blackbody spectrum with peculiar characteristics, that lead theoreticiens to suggest  we are observing for the very first time the two different photospheres of photons with different polarization properties (i.e. the so called ordinary and extraordinary waves which are expected in a strongly magnetized medium - Israel et al. 2008). This would be an unprecedented observational confirmation of our understanding of wave propagation in strong field!

However, the suggestion must be corroborated by a detailed treatment of radiative transfer in the trapped fireball: the lack of this important analysis prevented up to now a quantitative comparison between theory and  observations (see e.g. Liubarsky et al. 2002), which is mandatory to

constrain the properties of the fireball. The main goals of this PhD project  are: i) to build a complete, self-consistent model for the transport of  radiation in the trapped fireball, and ii) to apply results to fit  observed burst spectra in order to validate the model and derive physical parameters. The student  will develop specific competences in high magnetic field physics, numerical radiative transfer and the application of theoretical models to observations. As a first step, he/she will derive

expressions of the relativistic scattering cross below resonance for a thermal distribution of electrons/positrons in a form suitable to numerical calculations. Secondly, a complete transfer code will be  developed, including non-conservative scattering.  Finally, a spectral archive (obtained varying the model parameters) will be produced and used to interpret all available/forthcoming bursts observations. This will be the first ever state-of-the-art model for burst emission spectra. 

Left: A picture of the Nasa Swift satellite showing the different instruments on board. BAT and the XRT observes high energy burst in the gamma-ray and X-ray band with high timing resolution. Right: BAT and XRT light curves obtained simultaneously during the burst ``forest'' of 2006 March 29. Different energy ranges are shown: 1-4 

and 4-10 keV for the XRT (panels X1 and X2, respectively), and 15-25 keV, 25-40 keV, 40-100 keV and >100keV for the BAT (panels B1, B2, B3, andB4, respectively). 

Relativistic jets from accreting black holes: are they baryonic or leptonic?

Dr S. Zane and Prof K. Wu 

Relativistic outflows are often associated with accreting into compact objects, in particular, black holes. These outflows are collimated, in the form  of jets. How these jets are launched is an resolved issue that challenge astrophysics for decades. Little is also know what exactly are in the jets. In most studies the jets are modeled as magneto-hydrodynamical flows of electron-proton plasmas.

However, there are also studies which argue that relativistic jets from accreting black holes are leptonic, i.e. they are electron-positron plasmas flows. Regardless of whether the jets are baryonic or leptonic, the high-energy contents in the jet material and the violent phenomena associated withe relativistic flows in jets, such as shocks and entrainment of the jets with the clumpy ambient material would give rise to electron-positron pair production. These pairs would imprint observational signatures. These signatures would provide useful diagnostics of the relativistic flow dynamics and the physical conditions in the jets, as well as how the jets are interacting with their environments. Pair production in relativistic jets has not been fully explored, especially in the context of jet-environment interaction and in the hybrid baryonic/leptonic settings. 

In the project, the student will develop structured jet models in which pair-production occur and calculate the associated radiative processes.  It is a theoretical project, which involves phenomenological modeling, analytical calculations and numerical computation. It aims to derive predictions that can be tested by current or future X-ray/gamma-ray observations and to provide useful working models that are applicable in other branches of astrophysics, e.g. astro-particle physics involving UHE cosmic rays and neutrinos.

Above: Artist's impressions of a black hole surrounded by an accretion disk that emits powerful jets in the direction of the spin axis. 

Physics of the Auroral Acceleration Region

Prof. Andrew Fazakerley

The aurorae (northern and southern lights) are beautiful, dynamic curtains of light seen in the night skies, usually in the polar regions. They are also the source of the Earth’s strongest radio emission, auroral kilometric radiation. Aurorae and auroral kilometric (AKR) radiation are also seen at other magnetised planets such as Jupiter and Saturn. The processes that accelerate the electrons that produce the aurorae remain mysterious, and spacecraft observations will are needed to test whether prevailing theories are valid. The evolution of the orbit of the ESA Cluster 4-spacecraft mission has recently enabled the spacecraft to make the first multi-point observations in the “Auroral Acceleration Region”, at 4,000 to 12,000 km altitude at auroral latitudes. Special operations are ongoing and are being conducted with the Cluster tetrahedron oriented so as to allow simultaneous measurements at different altitudes on closely neighbouring magnetic field lines, to search for evidence of electron acceleration and the processes that cause it – for example, are electric potential drops along the magnetic field occurring in this region? The campaign is also designed so that some spacecraft can localise sources of emission of AKR while it is hoped that other spacecraft will fly through the sources, allowing definitive tests of the theories of AKR generation by unstable electron distributions. Cluster’s PEACE electron instruments are provided by MSSL-UCL and are providing a key dataset in AAR studies. The proposed PhD research will involve surveying the AAR dataset, and using data from PEACE and other instruments to address questions about what exactly happens in the auroral acceleration, and how the aurorae are ultimately driven by events in the magnetosphere.

Preparing for the Solar Orbiter Mission: Studies of the Properties of Solar Wind Charged Particle Populations and their Links to the Sun 

Prof. Chris Owen

UCL/MSSL is the Principal Investigator Institute on an international consortium providing the Solar Wind Analyser suite (SWA) of instruments for the ESA Solar Orbiter mission, due for launch in 2017. SWA will sample electron, proton, alpha particle and heavy ion populations at various distances down to 0.28 AU from the Sun (i.e. around a quarter the distance from the Sun to the Earth). In particular, UCL/MSSL is designing and building the electron analyser system (EAS) for the SWA suite. In order to prepare for the mission, and to be able to use the 3 sensors to make optimum measurements in the solar wind, we would like to undertake studies of the nature of the solar wind particle populations, their variability and their links to the Sun using, where relevant, data from existing in-orbit missions.

For example, it is known that the solar wind electron population in general consists of 3 components:  A 'core' population of the coldest electrons which is nearly isotropic - approximately the same flux of electrons of a given energy may be detected in any direction; A 'halo' population occurs at somewhat higher energies, and shows a slight shift in average velocity with respect to the core, and thus provides a 'heat flux' in the solar wind; Finally, a 'strahl' population is often seen as a more energetic beam of particles streaming along the magnetic field. Together these different electron populations contain information about the processes occurring at the source region on the Sun, the magnetic connections of the sampled plasma back to the Sun and on the plasma processes (e.g. turbulence, wave-particle interactions and magnetic reconnection) which may be occurring within the solar wind itself. Separating the effects of these processes is a complicated task requiring high-cadence, high resolution data of the type available during burst modes from the UCL/MSSL-built PEACE electron spectrometers on the 4 Cluster spacecraft when one or more of the spacecraft are located in the solar wind.   A highly mission-relevant PhD project would, for example, use these data to explore the nature and variability of the electron populations, using the multi-point measurements to determine the level of variation between spacecraft.

An alternate mission-relevant project would address the links between the heavy ion measurements in the solar wind and the measurements of the Sun itself available from ultra-violet imaging and spectroscopic telescopes.  Establishing such links between the SWA measurements of ion composition and the remote sensing measurements of the Sun has been identified as critical for the success of the Solar Orbiter mission.  Thus learning what can be done now, with existing datasets, will be invaluable during the post-launch analysis phase.  Such a project would benefit from the ready collaboration possible with researchers in the UCL/MSSL Solar Physics Group which possesses expertise in analysis of the remotely sensed observations.

The results of such projects are critical as preparation and inputs into the ESA Solar Orbiter program, and the student will thus also be an integral part of the MSSL instrument-build and science-planning teams, with the responsibility of making scientific inputs to those processes. There will also be opportunity to collaborate with our partners in France, Italy and the USA, who will provide the Heavy Ion Sensor and Proton-Alpha Sensor for the SWA suite.

Filament formation in solar atmosphere

Dr. Lucie Green & Dr. David Williams

Filaments are a fundamental structure in the magnetised solar atmosphere, forming in regions of both intense and weak magnetic field. Observationally they are manifested by collections of relatively cool and dense plasma which is suspended against gravity in the million degree solar atmosphere.

Over the last couple of decades, descriptions of filaments have progressed from simplified 2.5 D models to highly dynamic structures where new areas of physics are now being applied to describe the observations. There are questions on, for example, the role of turbulence and instabilities in a dense, magnetised, partially ionised plasma.

This project will work on the physical mechanisms which lead to the formation of filaments. This involves understanding how a magnetised plasma evolves at the boundary between a gas pressure-dominated domain (in the lower solar atmosphere) and the domain where the magnetic pressure dominates (mid-solar atmosphere), and studying the evolution of the associated magnetic structures, and the partially ionised plasma that fills them. This project will make use of state-of-the-art multi-spacecraft observations, including the newly-launched Interface Region Imaging Spectrometer mission, to study the plasma parameters within the filament and in its environment, to understand the genesis of these structures.

Photoelectron-driven escape at Venus, Mars, moons and comets

Prof. Andrew Coates

Venus has a thick atmosphere, with an ionosphere produced by photoionization of atoms and molecules by sunlight. When an ion is produced from a neutral, a photoelectron is also produced. The energy of the photoelectron is determined by the solar spectrum, subtracting the ionization potential. The energy spectrum of the photoelectrons therefore provides an unique energy spectrum by which ionospheric plasma can be uniquely recognized. The photoelectrons are more energetic than the ambient electrons and set up an electric field which causes plasma escape – an important process in atmospheric evolution. A similar process occurs at any solar system object with an atmosphere. We will examine photoelectrons in different solar system contexts using data and models.

We made the first detailed measurements of photoelectrons in the Titan and Venus ionospheres (Coates et al., 2007, 2008), studied more events at Titan (Wellbrock et al., 2012) and compared these at several objects including Titan, Mars and Earth (Coates et al., 2011). As at all of these objects, the observation of photoelectrons far from their production location indicates a magnetic connection to the ionosphere. Recently we used these observations to study plasma escape at Titan (Coates et al., 2012). Ionospheric photoelectrons are also expected at Rosetta’s target comet Churyumov-Gerasimenko.

The next step is to perform statistical studies of several years of data from Venus Express, Cassini, Mars Express and from the upcoming Rosetta mission to determine the morphology of photoelectrons at each of these environments. This will enable a detailed investigation of the role that photoelectrons play in plasma escape from these objects. The first step is to search the data for photoelectrons and build up 3D pictures of their locations. Escape rates will then be estimated and comparisons with models made.

Project phases

1. Develop techniques for detecting photoelectron signatures.

2. Determine 3D morphology of photoelectron observations at different objects

3. Estimate escape rates and compare with models

Work

• Data analysis ~ 80%

• Computer modelling ~ 20%

Data

Venus Express, Cassini, Mars Express, Rosetta

Photoelectrons and hidden plasma populations in Saturn's inner and middle magnetosphere

Prof. Andrew Coates

Energetic particles in Saturn's radiation belts produce a large background signal in the detectors of the CAPS instrument on the Cassini spacecraft. We are developing techniques to characterise and remove this noise from the measurements but they are in the early stages of development. We also do not understand the details of how the radiation produces the background signal, and especially how changes in the radiation environment affect the background.

The first part of this project will be to build a 3D computer radiation model for the CAPS instrument and the Cassini spacecraft. Measurements from Cassini and models of Saturn's radiation belts will be used to calculate the radiation falling onto the CAPS detectors and so calculate the noise level. These calculations will be compared with real measurements of the noise level. This will help us to understand how radiation affects the CAPS instrument and produces the noise we see in measurements. The detectors inside CAPS are called microchannel plates (MCPs) and how they are triggered by radiation is not well known, not just for CAPS but for many other types of instrument. The second part of the project will involved numerically modelling an MCP detector and bombarding the model detector with radiation to calculate the efficiency at which a particle of a particular type and energy will trigger a signal in the MCP.

The third part of the project will use the first two projects to properly subtract the radiation-induced noise from the measurements and study the real plasma particle signals in the data. A number of real plasma populations may be hidden by this noise and through detailed analysis we will be able to identify and characterise them. One of these populations is a population of photoelectrons. The ionisation of neutral molecules by extreme UV photos produces photoelectrons with a characteristic energy and spectrum which can provide valuable clues to understand the underlying neutral/plasma photochemistry. Photoelectrons are seen throughout the inner region of Saturn's E-ring and can provide important information on the neutral/plasma chemistry occuring in that region of Saturn's magnetosphere which can be used to validate models. In this part of the PhD you will develop techniques to automatically identify and measure the properties of photoelectrons in Saturn's inner magnetosphere. These measured properties will be analysed statistically, compared with models, and used to examine seasonal, day/night, and other temporal variability in Saturn's E-ring. Further work can involve studying photoelectrons in the ionospheres of Mars, Venus and Titan.

Project phases

1. 3D modelling of the Cassini CAPS instrument and spacecraft, use data and model radiation belts to calculate the noise level which will be compared with data.

2. Numerical modelling of an MCP detector to various types of radiation (electrons, protons, gamma rays) - calculation of efficiencies for detection.

3. Accurate subtraction of noise from the inner and middle magnetosphere of Saturn to study plasma particles that are hidden or hard to study due to noise.

Work

• Data analysis ~ 40%

• Computer modelling ~ 60%

Data

Cassini, Galileo

Ice grain trajectories in the Enceladus plume

Dr. Chris Arridge & Dr. Geraint Jones

The Cassini Plasma Spectrometer instrument has detected tiny nanometre-scale dust grains in a plume of water vapour, ice and dust originating from the south pole of Saturn's icy moon Enceladus. We have developed an initial computer model for how these grains move after leaving the interior of the moon. In this project this model will be further developed and refined with the results compared with observations. These comparisons will help to understand which observed dust grains are coming from what location on the moon. The development of the model will also need to account for electrostatic charging of the dust grains in the space environment near Enceladus. If these grains become highly charged they can literally be torn apart by the resulting electrostatic forces, so further thesis work in this area could involve collaboration with other groups at UCL to understand how these grains can be disrupted.

Project phases

1. Develop computer model for dust grain motion and charging and compare with observations.

2. Determine the source on Enceladus where the positive and negative grains emerge from.

3. Study dust grain disruption due to electrostatic forces.

Work

• Computer modelling ~ 70%

• Data analysis ~ 30%

Data

Cassini

Plasma heating in the magnetospheres of Jupiter and Saturn

Dr. Chris Arridge

The plasma found in the magnetospheres of Jupiter and Saturn largely originates in the natural satellites of these planets. After being added to the magnetosphere the plasma is typically very cold ~several eV in energy, but somehow this plasma is heated to tens of keV (>4 orders of magnitude). The exact processes responsible for heating this plasma is not well understood. This is an outstanding problem in astrophysics and is not restricted to understanding the magnetospheres of Jupiter and Saturn. In this project you will research the effectiveness of different plasma heating mechanisms. Initially the first study will reproduce and extend a study using data from Jupiter which shows that weak magnetohydrodynamic turbulence can heat plasma at Jupiter. You will extend this study to incorporate more data and more physics. This can be extended to Saturn and the results compared with observations and the Jupiter results. The second project involves examining how electrons in Saturn's magnetosphere achieve a similar temperature to protons. Evidence for a similar effect at Jupiter can be examined and understood. The third project involves the investigation of an additional heating mechanism which depends on the interests of the student but options include: plasma chemistry, acceleration in thin current sheets, and wave particle interactions.

Project phases

1. Study plasma heating due to weak MHD turbulence in the magnetospheres of Jupiter and Saturn using data from Galileo and Cassini.

2. Study how electrons heat to similar temperatures as protons in the magnetosphere of Saturn.

3. Study third heating mechanism (student’s choice).

Work

• Data analysis ~ 70%

• Computer modelling ~ 30%

Data

Cassini, Galileo, Voyager, Ulysses, Pioneer

Dust-Solar Wind Interactions

Dr. Geraint Jones

Data from several spacecraft studying the solar wind flowing outwards from the Sun have revealed the presence of interplanetary field enhancements. These are increases in magnetic field strength that follow a thorn-shaped profile, and last from minutes to hours. The most likely causes of these perplexing events are thought to be trails of relatively massive comet dust lying between the Sun and the spacecraft. These trails are formed of large particles that spread around comets’ orbits but are too massive to be accelerated away from the Sun due to radiation pressure, and are observable along several short-period comets’ orbits in the thermal IR. Such particles are observed at Earth as annual meteor showers when our planet traverses dust trails.

The project will involve an extensive survey of magnetic field data from several spacecraft to search for these signatures of comets' dust trails, characterizing their features and locations. By comparing the positions of the enhancements found to the orbits of known comets, an attempt will be made to determine the sources of the enhancements, and to help identify the physical processes that cause the field enhancements to form. An understanding of these features should lead to a better understanding of dust particles’ physical characteristics, and their potentially significant effect on the solar wind.

Project phases

1. Search through solar wind datasets for interplanetary field enhancements

2. Write code to perform a semi-automated search for these events (optional).

3. Analyse the bulk observations from this survey; attempting to link known comets and their dust trails with the solar wind.

4. Explore possible formation mechanisms through theoretical and/or simulation studies.

Work

• Data analysis ~ 60%

• Data reduction ~20%

• Computer modelling ~ 20%

Data

Cassini, ACE, Wind, Helios, Galileo, Voyager, Ulysses, Pioneer

In Situ Studies of Comet-Solar Wind Interactions

Dr. Geraint Jones &  Prof. Andrew Coates

The Rosetta spacecraft’s arrival at its target comet in early 2014 will allow the study of the interactions between the solar wind and a weak source of fresh ions. As the spacecraft follows comet Churyumov-Gerasimenko as it plunges towards the Sun, the nature of this interaction is expected to change dramatically as the comet’s gas production rate increases due to greater solar heating.

This project will involve the analysis of data from the Rosetta mission, together with complementary observations of comet-solar wind interactions at objects covering a wide range of gas production rates obtained by both targeted and serendipitous spacecraft encounters. Our group led the building of a key plasma instrument for the Giotto spacecraft that visited comets Halley and Grigg-Skejllerup. Other spacecraft equipped with plasma instrumentation have also visited or crossed the tails of comets Halley, Giacobini-Zinner, Borrelly, Hyakutake, McNaught-Hartley, and McNaught. We plan to make direct comparisons between data obtained by those spacecraft and the exciting new information from Rosetta, allowing us to better characterise the effects of varying gas production rate and solar wind conditions on the modes of interaction between comets and the solar wind. 

Project phases

1. Study data returned by the Rosetta spacecraft at Comet Churyumov-Gerasimenko.

2. Compare the data to results obtained by the Giotto Johnstone Plasma Analyser and other instruments at two comets.

3. Conduct a survey of data obtained by other missions

4. Characterize the results as a function of comet gas production rate and solar wind conditions, comparing to model results where possible.

Work

• Data analysis ~ 60%

• Programming of Giotto analysis software ~20%

• Computer modelling ~ 20%

Data

Rosetta, Giotto, Ulysses, Deep Space 1, International Cometary Explorer, Suisei, Sakigake, Vega-1 & 2

PAH mapping of the martian polar ice-caps and its cosmochemical implications

Prof. J.-P. Muller

Analysis of image spectrometry data of Cassini's satellites Iapetus & Phoebe from the Cassini/VIMS instrument revealed the presence of large quantities of PAHs in a mid-IR band (Cruikshank et al., 2008). PAHs are created as a result of radiation interactions with interstellar dust clouds and are often observed in Carbonaceous Condrites. The Viking Lander observations found no detectable trace of PAHs in martian soil samples contrary to what was expected at the time. Recent NASA MRO-CRISM observations appear to reveal PAH signatures over polar regions. The proposed project will look in detail at an imaging spectral analysis and will examine possible CO2-water ice mixtures to determine what quantities of PAH would be required to give the signal detected. Further CRISM data will be analysed to determine if such PAH signatures are present elsewhere on the planet. The relationship of these features to CO2 geysers will also be examined.

Isotopologues of Carbon measured from spectrometry on Mars and the Earth

Prof. J.-P. Muller

The advent of ultrafine spectroscopy (<0.01nm) raises the possibility of measuring atmospheric isotopic ratios of Carbon to determine its source. Recently Fletcher et al. (2009) have demonstrated the retrieval of isotopologues of Carbon in Methane near and far-IR measurements of Saturn's atmosphere from the Cassini/CIRS instrument whilst Robert et al. (1010) showed similar retrievals for CO2 on Venus from Venus Express/SOIR and Villanueva et al.(2008) from ground-based measurements of CO2 on Mars. Higher quality solar occultation measurements are also possible for the terrestrial atmosphere which can be directly applied to Mars (Leblanc et al., 2008). In 2016, the ExoMars Trace Gas Orbiter will be launched by ESA/Roscosmos including a Russian spectrometer capable of making measurements of methane and possibly isopologues. This project will focus on the development of retrieval methods for isotopologues of methane and CO2 using the ACE-FTS and Cassini/CIRS as a pre-cursor to EMTGO16. There will also be some scope for participating in field trials of these retrieval methods at UCL-Australia.

How Does Solar Activity Influence Winter Climate? 

Prof Mark Saunders and Dr Lidia van Driel-Gesztelyi

The Northern Hemisphere winters of 2008/9 and 2009/10 were unusually cold and snowy. The timing of these events close to a deep minimum in solar activity has raised interest in the influence of low solar activity on cold winters. Many studies going back centuries have examined the relationship between solar activity and aspects of climate. The weight of plausible evidence leaves little doubt that changes in solar activity do influence the Earth’s climate. However, the nature and importance of this link remains unclear. In particular a convincing and consistent physical mechanism (or mechanism chain) for how solar activity can influence winter climate is still missing. 

Using the best long-term and high temporal-quality solar irradiance data, Earth satellite data and Earth surface observations, the project will attempt to establish a causality chain between changes in solar activity and changes in northern hemisphere surface winter climate. Focus will be given to the role of the stratosphere and the propagation of zonally averaged zonal wind anomalies from the tropical stratosphere to the high latitude stratosphere during October and November. Once established at high latitudes in early winter this circulation may extend down through the troposphere to contribute significantly to the winter monthly and seasonal Arctic Oscillation and thus to winter climate. But what causes the poleward propagation from the tropical stratosphere to begin and how do changes in solar activity contribute to or facilitate this? What is the role of the quasi-biennial oscillation in establishing or modulating the conditions which enable this propagation to occur? Do solar influences offer predictability of winter climate? These are the questions the project will empirically address.

Technology Decision Making and Risk Management in Space

Dr Michael Emes

Although space technology is often thought of as ‘cutting edge’, the harshness of the space environment and very limited capacity to respond to technological failure often dictates a quite conservative approach to technology adoption. This project would investigate the processes involved in selecting and exploiting technology for space missions. It will also investigate how risk is managed for space missions with a view to developing best practice in this area.

Typical Research Activities

The project might include the following activities:

• Interview MSSL staff and employees of space organisations such as EADS Astrium, SSTL, ESA and NASA to discuss technology maturity rules. Investigate the process for getting technology selected for space missions, including selection criteria.

• Read published literature to explore how the adoption of innovations in space differs from other industries, and the relationship between ground-based and space-based technologies. 

• Investigate how ground-based technologies get modified for use in space, and how space innovations find their way into terrestrial technologies,. What are the benefits of space for society?

• Explore trends in space missions and space technologies, trends in terrestrial technology use, and potential societal change and explore different scenarios for the needs of future space missions, whether scientific or commercial.

• Apply a systems approach to understand how risk for space technology is managed and to investigate decision making processes including how the time, cost, risk, quality and scope of technological processes are traded

• Investigate barriers to effective decision making in technological processes, including cognitive traps and effectiveness of group decision making

Anticipated research outputs

• Assessment of best practice in technological decision making

• How to deal with risk and uncertainty in technological decision making

• Identification of barriers to effective technological decision making and how these can be overcome

• Summary of process for developing and proving technology for space

• Summary of routes by which space technologies are exploited on earth, and 

• Reflections on value of space technology research

• Recommendations for improving process for developing/proving technology for space

• Roadmap for which technologies should be invested in now in order to support future space missions.

Suitable Background of Student

Good first degree in maths, physical sciences or engineering. Some knowledge of the space sector and the subjects of systems engineering, project management, technology maturity and/or risk management desirable but not essential.