PhDs in Planetary Physics

Oxford’s Planetary Physics group specialises in the exploration of planetary atmospheres and surfaces, with expertise ranging from hardware development to spectral analysis; ground-based astronomy to spacecraft operations; and numerical simulations of planetary climate to laboratory experiments of geophysical fluid dynamics. Our interests extend from the environments found in our own Solar System to the extreme conditions found in Extrasolar Planets and Brown Dwarfs. An overview of our research can be found on the Planetary Science page.

Several projects are available within the group in the coming year. They can involve the measurement and modelling of visible and infrared spectra of planetary objects, using available data to understand and model their environmental conditions (atmospheric dynamics, composition and clouds; thermophysical properties and compositions of surfaces), making laboratory measurements of the spectral behaviour of candidate materials, or modelling the behaviour of planets in extreme conditions.

2017 project descriptions

Infrared remote sensing of the Ice Giants: atmospheric temperature, composition and clouds

Supervisor: Patrick Irwin (AOPP)
Project ref: AOPP/PGJI/1/2017

Voyager 2 flew past Uranus and Neptune in 1986 and 1989, and provided our only close-up views of these ice giant worlds. Now, a quarter-century later, the ice giants are recognised as key destinations for future planetary missions and as our closest examples of a planetary class that appears commonplace throughout our galaxy. The Voyager flybys revealed dynamic worlds quite unlike the familiar banded structures of Jupiter and Saturn, but the brevity of these encounters prevented detailed scrutiny. Uranus was shown to be rather sluggish, whereas Neptune featured dynamic cloud activity and vortices. This difference has never been satisfactorily explained and subsequent ground based observations have since suggested that the activity on both of these planets varies hugely with time. This project aims to construct a three-dimensional understanding of an ice giant atmosphere to connect activity in the tropospheric weather layer (where convective clouds form and are sheared apart) to the middle atmosphere (the stratosphere, dominated by wave activity and photochemistry). The candidate would attempt to link changes in cloud activity and albedo in reflectivity spectra (wavelengths < 3 µm) with the temperature and composition of the ice giants, as measured in thermal-infrared spectra (wavelengths> 5 µm), to reveal the underlying dynamics and circulations of these ice giant atmospheres.

This project will utilise infrared observations from a variety of ground-based and space-based observatories. Uranus observations taken near spring equinox in 2007 by the Spitzer Space Telescope will be used to measure the longitudinal variations of temperature and composition in the stratosphere, attempting to relate these variations to wave activity generated by tropospheric weather. As well as revealing the chemistry of Uranus’ middle atmosphere, this will also aid in our understanding of vertical energy transport processes on the ice giants. In addition, ground-based infrared imaging and spectroscopy of the ice giants from the world’s leading observatories (e.g., Gemini, VLT and Subaru) will be used to determine the spatial variation, vertical distribution and temporal evolution of cloud activity, relating this to the derived thermal structure to understand the condensation processes at work in these frigid atmospheres.

The key result of this project will be a self-consistent picture of the circulation and cloud-forming processes at work on the ice giants, paving the way for future atmospheric studies by visiting spacecraft. The successful candidate would be joining a well-established planetary data analysis group that is actively involved in observational astronomy and planetary missions (e.g., the Cassini mission at Saturn). Analysis of spectral data will be performed using the suite of radiative transfer and retrieval software developed at Oxford, collectively known as NEMESIS. The candidate would gain experience of acquiring, reducing and interpreting infrared imaging and spectroscopy from a range of world-class telescope facilities, both on the ground and in space.

This project will be computationally intensive using Fortran, IDL and others, so a physics/computing/mathematics background is preferred, and a first degree in Physics or Mathematics is required.

VLT/MUSE observations of the Giant Planets

[b]Supervisor: Patrick Irwin (AOPP) [/b]
Project ref: AOPP/PGJI/2/2017

Credit: ESO/MUSE Consortium: Jupiter observed with VLT/MUSE in March 2014Giant planet clouds are amongst the most beautiful and complex phenomena displayed by the planets of our solar system. Their spatial distribution reveals the forces and energy exchange mechanisms (e.g., moist convection) shaping the banded appearance of the planetary weather layers; their vertical structure tells us about the composition and cloud microphysics; and their colour reveals the chemical alteration of aerosols in a giant planet atmosphere. While most clouds are white, the clouds of Jupiter and Saturn are coloured with various hues of yellow and red, but the nature of these colours, or ‘chromophores,’ has yet to be determined, and remains an enduring mystery.

The recently commissioned MUSE (Multi Unit Spectroscopic Explorer) instrument at the VLT (Very Large Telescope) in Chile, has provided an unprecedented opportunity to study the clouds, dynamics and composition of the giant planet atmospheres at a spatial and spectral resolution never before possible. MUSE measures spectral ‘cubes’ in which each pixel of the 300 x 300 field of view is a complete spectrum covering the range spectral 465 to 1000 nm. These ‘cubes’ will allow us to map the spatial distribution of the clouds and colouring agents, estimate cloud top levels and determine spatial variations in methane abundance (for Uranus and Neptune) and ammonia (Jupiter and Saturn). While other ground-based and space-based instruments can provide partial coverage of these wavelengths (usually as images in discrete filters), only MUSE provides the unique combination of spatial and spectral coverage, which makes it a very powerful tool for studying clouds in giant planet atmospheres.

In this project, the student will analyse existing VLT/MUSE Giant Planet observations. He/she will also participate in proposing and reducing future observations, and will gain excellent experience in telescopic observations and analysis. The spectral cubes will be analysed with a sophisticated multiple-scattering radiative transfer model, NEMESIS, previously developed to model observations of solar system planets. The timescale of the project would mean that the student would have real data to analyse from the start. These data will be analysed to look for seasonal changes and also monitor occasional cloud upheaval events, such as the great storm on Saturn in 2010, the NEB outbreak on Jupiter in 2012 and the recent cloud outbreak on Uranus in 2014, which was so bright that it was visible to amateur astronomers. In addition, our planned VLT/MUSE observations (which will run until the middle of 2017) will provide invaluable context observations for the NASA/Juno mission, which arrived in Jupiter orbit in July 2016. This spacecraft has been placed into a polar orbit, with a low periapsis over Jupiter’s north pole. The mission is primarily designed to determine Jupiter’s internal structure by mapping its gravitational field, but remote sensing cameras also observe narrow ‘strips’ of Jupiter as the spacecraft flies over the north pole. Interpreting these observations requires that we know how the observed ‘strips’ relate to the overall appearance and cloud structure of Jupiter. While simple ground-based imaging will be able to relate the strips to the wider context, only VLT/MUSE will be able to provide the spectral component, relating any composition/chromophore changes detected by Juno with the wide Jovian atmosphere. Thus, VLT/MUSE is able to provide unique ‘ground-support’ to the Juno mission, and working on this project would embed the student within the global community of giant planet astronomers.

This project will be computationally intensive using Fortran, IDL and others, so a physics/computing/mathematics degree is preferred.

Modelling the spectra of exoplanets

[b]Supervisors: Patrick Irwin (AOPP) and Suzanne Aigrain (Astrophysics)[/b]
Project ref: AOPP/PGJI/3/2017

The discovery of exoplanets in 1995, just twenty years ago, has ushered in a new age in scientific exploration. Over 1900 exoplanets have now been discovered and the study of these worlds has profound implications for our understanding of human evolution and our place in the universe. New missions, such as the James Webb Space Telescope (JWST), due for launch in 2018, will return better-than-ever transit spectra of exoplanets, where the planet passes either in front of or behind the host star. In parallel with this ground-based direct-imaging spectroscopy instruments VLT/SPHERE and Gemini/GPI promise to revolutionise the field of ground-based exoplanet spectral measurements by recording the reflection/emission spectra of some of these worlds directly. Further in the future, dedicated exoplanet missions such as the proposed Ariel spacecraft will enable greatly improved atmospheric characterisation through more precise transit spectra measurements.

Modelling radiative transfer in these atmospheres underpins the scientific exploitation of these observations, but many challenges are faced compared with Solar System analyses, the most important being the very high atmospheric temperatures of some of the ‘Hot Jupiters’ and also the absorbing and scattering effect of clouds, whose broad spectral features can mask and obscure gaseous features. In this project the student will take Oxford’s existing sophisticated radiative transfer and retrieval model, NEMESIS, which was first developed for solar system planetary analysis, and use it to model the observed spectra of exoplanets to determine their gaseous composition and thermal structure. This will be done both with our traditional optimal estimation approach and also using the Markov Chain Monte Carlo and nested sampling methods, which have recently been implemented within the NEMESIS framework. In particular, accurate modelling of condensates in exoplanetary atmospheres is now thought to be crucial in reliably interpreting exoplanet spectra. The student will thus investigate the influence of including different cloud species on the spectra produced by NEMESIS, and consider the likelihood of occurrence of such clouds in exoplanetary atmospheres. These studies will be used to inform how future observations of JWST and other possible missions should best be designed to maximise their scientific return. With a start date in 2017, the student would be well placed to analyse data collected during JWST’s first year of operations, and then apply for further time.

This project will be computationally intensive using Fortran, IDL and others, so a physics/computing/mathematics degree is preferred.

Studying Martian water vapour using the ExoMars Trace Gas Orbiter

[b]Supervisors: Patrick Irwin (AOPP) and Colin Wilson (AOPP)[/b]
Project ref: AOPP/PGJI/4/2017

Europe’s ExoMars missions seek to establish whether there is, or has been, any form of life on Mars. The first spacecraft of the ExoMars programme is the Trace Gas Orbiter (TGO), which successfully arrived at Mars in Oct 2016 and will commence regular science observations in March 2018. TGO and its scientific payloads are optimised for detection and mapping of trace gases: these include gases like methane which might be biologically produced, but also includes water vapour. Water vapour is the most important volatile on Mars; its distribution affects climate, atmospheric chemistry and habitability.

In this project, the student will map the spatial and temporal variations of water vapour, through analysis of infrared spectra obtained by TGO’s Russian-led ACS (Atmospheric Chemistry Suite) spectrometer suite. ACS includes three different spectrometers and at least two different observing geometries; intercomparison of water retrievals obtained using the different ACS observation types, and intercomparison with other datasets, will be performed to check the consistency of the results. The improved understanding of the distribution and variability of water vapour on Mars will be fed into climate models, will help identify potentially habitable underground niches, and will inform landing site characterization for the ExoMars rover in 2020.

This project will be computationally intensive using Fortran, IDL and others, so a physics/computing/mathematics degree is preferred.

Exoplanet climate dynamics

Supervisor: Raymond Pierrehumbert (AOPP)
Project ref: AOPP/RTP/1/2017

The newly discovered exoplanets present possibilities for a diverse range of climate situations not encountered in our own solar system. The demands of this new subject challenge the limits of current modelling capabilities, and while they involve the same underlying physical components as are familiar from the Solar systems, these components are present in novel combinations. This project involves a range of modeling and theoretical activities aimed at understanding the new climates. There is a particular emphasis on identifying potentially observable consequences of various exoplanet climate phenomena.

The primary focus of the project is on planets in the Earth or Super-Earth size class. Surveys of planetary density have shown that the latter class of planets need not have a rocky surface, and might instead by fluid planets more properly thought of as mini-Neptunes. One of the goals of the project is to further develop the group’s exoplanet general circulation model to cover additional planetary configurations, and to explore the climate behavior. Questions of interest include: (1) Seasonal/diurnal cycle on planets in low-order spin/orbit states with length of day comparable to length of year, (2) dynamics and thermodynamics of condensible-rich atmospheres, (3) dynamics governing subsaturation of condensibles, (4) dynamics governing the pattern of cloud cover. General circulation modeling studies will be supplemented by use of a hierarchy of simpler climate models.

This project requires a thorough understanding of fundamental physics, including thermodynamics, mechanics and electromagnetic radiation, as well as a facility with analysis of mathematical models. Familiarity with physical chemistry is also desirable. Hence, a first degree in Physics, Mathematics or a related discipline is required. The project involves considerable use of computational techniques, so basic familiarity with numerical analysis and familiarity with programming techniques in some computer language is required. The main programming languages used are Python and Fortran, but prior experience with these specific languages, while desirable, is not required.

Modelling and observations of large-scale storms and vortices on Jupiter and Saturn

Supervisor: Peter Read (AOPP)
Project ref: AOPP/PLR/1/2017

The atmospheres of Jupiter and Saturn are characterized at their cloud tops by patterns of winds organized into many intense, parallel jet streams, aligned east-west, within which we observe a rich diversity of eddies, vortices, waves and convective storms. The origin of these eddies is often far from clear, and the whole problem is compounded by our inability to observe their structure below the tops of the NH3 clouds that visualize them. Recent modeling and observational studies (in Oxford and elsewhere) suggest that the zonal jet streams owe much of their origin to nonlinear interactions with the eddies themselves, but the details are still not fully understood. The structure of many of the large eddies in the vertical is also quite uncertain, so we need to rely on fundamental theory and models to infer what may be going on in the deep atmosphere.

In this project, we will make use of a numerical model of the atmospheres of Jupiter and Saturn, based on the MITgcm, that will have sufficient horizontal and vertical resolution to explore the possible structure and origin of vortices, waves and storms in association with strong jet streams. The model has been under development in Oxford for some time now, and includes a number of facilities to represent the main thermodynamic forcing processes (radiative transfer, convection and moist processes) and the formation and transport of clouds. It is currently being optimized for global simulations at moderate resolution, but in the present project it is envisaged to use the model to cover just a limited region of the atmosphere in the horizontal with very high spatial resolution. Model simulations will be carried out to explore analogues of features such as Jupiter's Great Red Spot and Oval BA, Saturn's "Ribbon Wave" and "Polar Hexagon", the giant convective storm of 2010, and compact polar vortices seen on both planets. Simulations will be compared with detailed observations of winds, temperature and other variables where possible, with the possibility of deriving new wind measurements from existing imagery of these features if required. The overall aim will be to try to identify conditions under which features resembling those observed can be reproduced within model simulations and to infer aspects of their vertical structure that may eventually be amenable to observational tests.

This project will be computationally intensive, using programming languages such as Fortran, IDL, MATLAB and others, so a physics/computing/mathematics background is preferred, and a first degree in Physics, Mathematics or a related discipline is required.

Modelling the atmospheres of slowly rotating planets

Supervisor: Peter Read (AOPP)
Project ref: AOPP/PLR/2/2017

Venus and Titan are planetary bodies that have substantial atmospheres but rotate relatively slowly compared to the Earth. This places their atmospheres in a very different dynamical regime from that of the Earth, and both are observed, for example, to rotate much faster about their planetary rotation axes than the underlying planet, quite unlike the Earth's atmosphere. The detailed mechanism that causes the atmospheres of these planets to "super-rotate" is beginning to become clear, and dynamical models developed recently (in Oxford and elsewhere) have begun to reproduce this basic behavior. From such models, it seems clear that the mechanism driving the strong super-rotation on Venus may be qualitatively different from the one most active on Titan, with Venus being strongly affected by the intense contrast in solar heating between the day- and night-sides of the planet. Such diurnal effects appear to be relatively weak on Titan however. These two bodies may also represent prototypes of classes of planets that may also be found orbiting other stars.

Despite these successes, even the most realistic and sophisticated models of the Venus atmosphere have proved unable to reproduce the observed structure of the super-rotation in its deep atmosphere, and a number of aspects of the circulation of both planets remain poorly understood. In this project, therefore, we will use a range of numerical simulation models to explore both the tropical and extra-tropical circulation of slow rotators such as Venus and Titan. These models will include both a highly idealized 3D general circulation model with simplified forcing parameterizations and a much more sophisticated model of the Venus atmosphere, based on the UK Met Office Unified Model. The latter includes realistic physical representations of radiative transfer in the Venus atmosphere, surface topography and the formation of clouds. One focus for Venus will be on improving the representation of the deep atmosphere, below the visible clouds, and its interaction with the underlying surface. Comparison with observations e.g. from ESA's Venus Express mission will be made wherever possible (and from the Cassini Orbiter for Titan) with the aim of identifying processes that can be evaluated in future space missions.

This project will be computationally intensive, using programming languages such as Fortran, IDL, MATLAB and others, so a physics/computing/mathematics background is preferred, and a first degree in Physics, Mathematics or a related discipline is required.

Exploring near Earth asteroids in the infrared, supporting NASA’s OSIRIS-REx sample return mission

Supervisors: Neil Bowles (AOPP) and Kerri Donaldson Hanna (AOPP)
Project ref: AOPP/NEB/1/2017

N.B. This replaces the project 'Exploring the Moon and asteroids in the infrared' previously posted.

The need to better understand the building blocks of our solar system has become a global mission as NASA, ESA, and JAXA have missions designed to characterise and in some cases sample Near Earth Asteroids (NEAs) some of the most primitive solar system bodies. NASA’s Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer (OSIRIS-REx) mission will be one of the first missions to a primitive asteroid in the solar system (1999 RQ36 also known as Bennu) and return with a sample from its surface [e.g. Lauretta et al., 2012]. OSIRIS-REx was successfully launched in September 2016 and is due to arrive in mid-2018 when it begins characterising Bennu’s surface in anticipation of selecting a sampling location. Thus, this studentship covers a critical time period of the OSIRIS-REx mission. Laboratory analyses of sample materials from Bennu’s surface will provide significant insights into the formation, survivability and nature of organic materials in our solar system, which could have formed life on Earth, as well as the physical nature and composition of such primitive bodies.

Orbital measurements of Bennu will be the first to characterize a primitive body in such detail to understand the morphology, thermophysical and photometric nature of the surface as well as its chemistry and mineralogy. Accurate determination of these parameters are essential to understanding the orbital evolution of Near Earth Asteroids and their potential as hazardous objects.

This project will fill a major need in the building of a reference set of laboratory spectra and help in the analysis of data as it is returned by the OSIRIS-REx mission. By making links to remote sensing data the proposed laboratory work will allow sample measurements of individual objects to be placed in their wider context of solar system evolution.

This project will be mainly laboratory based with some significant computing and data analysis elements. A good first degree in Physics or Earth Sciences is required and a strong interest in laboratory and remote sensing techniques is preferred.