DPhil (PhD) Projects in Planetary & Exoplanetary Physics 2018

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, and an overview of exoplanet research at Oxford can be found on the Oxford Exoplanet page.

Several projects are available within the group in the coming year. They typically involve the measurement and modelling of visible and infrared spectra of planetary objects, using these data to understand and model their environmental conditions (atmospheric dynamics, composition and clouds; thermophysical properties and compositions of surfaces). Next year we shall be looking for students in the following areas:

  • The transit spectra of exoplanets
  • Characterising the thermal alteration history of carbonaceous meteorites to help interpret data from NASA’s OSIRIS-REx asteroid sample return mission
  • Re-constructing Primitive Meteoritic Materials in the Laboratory to support remote sensing of asteroids and comets
  • Ground and space-based telescope observations of the Ice Giants (Uranus and Neptune)
  • Spectroscopic monitoring of Jupiter’s atmospheric dynamics and chemistry to support planetary missions
  • Dynamical modelling of storms and eddies in the atmospheres of Jupiter and Saturn
  • Modelling the circulation of slowly rotating planets, such as Venus and Titan
  • Climate modelling of terrestrial planets fluid or rocky super-Earths
  • European Research Council project EXOCONDENSE, on effect of condensable atmospheric constituents on climate dynamics of exoplanet atmospheres.

2019 project descriptions

Modelling the spectra of Exoplanets

Supervisor: Patrick Irwin (AOPP)
Project ref: AOPP/PGJI/1/2019

The discovery of exoplanets in 1995, just over twenty years ago, has ushered in a new age in scientific exploration. Over 5000 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), now due for launch in 2021, will return better-than-ever transit spectra of exoplanets, where the planet passes either in front of or behind the host star, and also allow direct-imaging observations. In parallel with this, ground-based direct-imaging spectroscopy instruments, such as VLT/SPHERE and Gemini/GPI, promise to revolutionise the field of ground-based exoplanet spectral measurements by also recording the reflection/emission spectra of some of these worlds directly. Further in the future, potential dedicated exoplanet missions such as the proposed Ariel spacecraft could enable greatly improved atmospheric characterisation through more precise transit spectra measurements, and missions such as WFIRST could record directly-imaged planetary reflection/emission spectra.

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 of these challenges are 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 Bayesian nested sampling methods, which have recently been implemented within the NEMESIS framework.

One area of focus may be accurate modelling of condensates in exoplanetary atmospheres is now thought to be crucial in reliably interpreting exoplanet spectra. The student would 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.

Another area of focus might be to do high spectral resolution modelling of exoplanetary data to search for the spectral signatures of at atmospheric gases. Such a study would use ground-based high-spectral-resolution observations.

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

Infrared remote sensing of the Ice Giants

Supervisor: Patrick Irwin (AOPP)
Project ref: AOPP/PGJI/2/2019

Voyager 2 flew past Uranus and Neptune in 1986 and 1989, and provided our only close-up views of these ice giant worlds. Now, more than a quarter of a 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 with atmospheres quite unlike the familiar banded cloud structures seen on 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’s 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, ESO’s Very Large Telescope (VLT) and Subaru), and also NASA’s James Webb Space Telescope (JWST), scheduled for launch in 2021, will be used to determine the spatial variation, vertical distribution and temporal evolution of temperature and cloud activity, to better understand the condensation processes at work in these frigid atmospheres. In particular, the MUSE instrument at VLT has a new Narrow Field Mode, which is ideally suited to studying the clouds and hazes of Uranus and Neptune. Recently acquired commissioning observations of Neptune have confirmed a latitudinal variation in Neptune’s methane abundance and we intend to apply for time to study Uranus’s clouds with this mode also.

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 recently completed 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 be involved with new observation proposals at ground-based observatories, such as VLT and 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.

Visible and Infrared remote sensing of the Gas Giants

Supervisor: Patrick Irwin (AOPP)
Project ref: AOPP/PGJI/3/2019

The clouds of the Solar System’s Gas Giants (Jupiter and Saturn) are amongst the most beautiful and complex phenomena displayed by the planets. 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.

To better understand these planets, we can turn to a number of ground-based and space-based observatories. ESO’s Very Large Telescope (VLT) in Chile, is equipped with a number of instruments, ranging from the visible to the infrared. For example, the MUSE (Multi Unit Spectroscopic Explorer) instrument 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 480 to 930 nm. These ‘cubes’ allow us to map the spatial distribution of the clouds and colouring agents, estimate cloud top levels and determine spatial variations of ammonia abundance. 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. At near-infrared wavelengths, VLT’s SINFONI instrument provides a similar near-infrared mapping spectroscopy capability, and the data can be used to better constrain vertical cloud structure. At even longer wavelengths, instruments such as VISIR provide thermal mapping that can be used to determine the vertical and spatial distribution of temperature and gaseous abundances. In addition to these ground-based facilities, NASA’s James Webb Space Telescope (JWST), scheduled for launch in 2021, is planned to make many observations of the gas giants over a wide wavelength range that will need to be understood and interpreted.

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 recently completed Cassini mission at Saturn). In this project, the student will analyse existing VLT/MUSE Giant Planet observations and participate in proposing and reducing future observations, gaining 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 used 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. In addition, our VLT/MUSE observations of Jupiter (which are ongoing) 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 is able to provide the spectral component, relating any composition/chromophore changes detected by Juno with the wide Jovian atmosphere.

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

More projects will be posted shortly.