Planetary and Exoplanetary Physics

Below is a list of available DPhil projects for planetary and exoplanetary physics. If you are interested in any of the following research areas, please contact the relevant supervisor directly as they will be happy to have a dialogue with you. Please note that additional exoplanet projects are available as a DPhil in Astrophysics (exoplanets and stellar physics).

Some projects may be filled as applications are reviewed, so we particularly encourage any candidates considering an application after the January deadline to contact prospective supervisors about available project options.

Neil Bowles
Project ref: AOPP/NB/1/

Oxford Physics are part of the international team helping to develop ESA's ARIEL Exoplanet space telescope due for launch in the late 2020s. ARIEL is a 1 m class telescope that will be located at the 2nd Earth-Sun Lagrange point to carry out the first detailed transit spectroscopy survey of more than 1000 exoplanetary atmospheres. Our group, supported by the UK Space Agency, are working on the optical ground test equipment to ensure that ARIEL can meet its strict stability requirements that will allow the mission once launched to untangle the signal of a planet’s atmosphere from that of its host star. We are looking for a student to join our team to work on the design, test and development of ARIEL’s optical ground test equipment. The student will then link the performance we can measure on the ground will to ARIEL’s predicted ability to characterise the atmospheres of planets around other stars.

This project will involve the joining our existing team to work on the development and testing of equipment for testing space instrumentation, including the optical instrumentation.  A first degree in physics/astrophysics or an engineering related discipline is required.

Neil Bowles
Project ref: AOPP/NB/2/

Understanding the surface characteristics of the Moon and comets through measurements in the thermal infrared provides important information on their geology and evolutionary history.  Our group here in Oxford Physics has a long history in developing space-based thermal infrared cameras and spectrometers and we are providing two similar instruments for NASA’s Lunar Trailblazer and ESA’s Comet Interceptor missions.

Lunar Trailblazer is a NASA SIMPLEX small satellite mission to the Moon that is due to launch in 2024 with two instruments, a near-infrared spectrometer (called HVM3) from NASA/JPL and the Lunar Thermal Mapper from Oxford Physics.  The Lunar Thermal Mapper (LTM) has a similar design to the thermal infrared module that is part of the multispectral camera, called MIRMIS, on ESA’s Comet Interceptor mission so the student will have the unique opportunity to become involved in both missions.

The student will join our Lunar Trailblazer and Comet Interceptor team. The project will involve working on the science, calibration and test of the LTM breadboard instrument that supports both missions, as well as the opportunity to work with existing data sets from missions such as NASA’s Lunar Reconnaissance Orbiter and ESA’s Rosetta mission to comet 67P.   The student should have a good first degree in a Physics/Engineering or Earth Sciences with a strong interest in space instrumentation.

Carly Howett
Project ref: AOPP/CH/1/

Saturn’s icy satellites are diverse and remain enigmatic, despite years of study by NASA’s Cassini mission. The satellites vary in colour, size, and activity. Some, like Mimas, are long dead and show the scars from years of impactor bombardment. While others, like Mimas’ neighbour Enceladus, have active plumes that send ice and dust into space. Understanding the surface of these targets is crucial in understand their role in the Saturn-system, how they interact with Saturn’s rings, high-energy particles, impacting populations, and even whether they could even host life.

Enceladus’ geysers erupt from four fractures that span its south polar region. The resulting plume escapes the moon, forming a ring around Saturn called the E-ring. Exactly why and how the plumes are formed is unknown, but the eruptive material is thought to come from a liquid water ocean, held beneath Enceladus’ icy surface. Whether this ocean supports life is arguably one of the greatest current mysteries of our solar system.

The high-energy electrons that orbit Saturn bombard the surface of Mimas, Tethys and Dione. This bombardment damages their water-ice surfaces, effectively gluing grains in the surface together, which stops it from cooling down at night as much as their surroundings. This surface alteration also changes its colour, making it appear more blue. How this bombardment alters with electron energy, surface depth, and whether such alteration could be occurring elsewhere in the solar system is still poorly understood.

Cassini studied the Saturn system from 2004 until 2017, during which time a wealth of data was obtained on Saturn’s icy satellites. I am seeking one DPhil (PhD) student to continue my work in analysing Cassini’s Composite Infrared Spectrometer (CIRS) data, specifically to analyse eclipse observations made of Saturn’s icy satellites. Eclipse observations are powerful because they allow the very surface (top few mm) of an icy world to be probed. This region is otherwise difficult to study, but yet vital to understanding everything that happens beneath it. Eclipse observations were made of most of Saturn’s icy moons, so could inform on how Enceladus’ plume recoats its surface, and how the very near surface of Mimas/Tethys/Dione is altered by electron bombardment.

The study of icy worlds has a strong future. The upcoming NASA mission “Europa Clipper” will launch in 2024 to study Jupiter’s icy world Europa, and NASA’s Lucy mission launches in late 2021 to study Jupiter’s Trojan asteroids. As a Co-I on both of these missions future opportunities exist for expanding into these targets. The successful candidate would be joining a well-established planetary science group, which is actively involved with many planetary missions and astronomy. International collaborations are include working with other modelling groups located in the USA and Switzerland.

The work will be computationally intensive, using programming languages like IDL and python, so a physics/computing/mathematics background is preferred, and a first degree in Physics, Mathematics or a related discipline is required.

Patrick Irwin
Project ref: AOPP/PGJI/1/2023

Uranus and Neptune, known as the “Ice Giants” are amongst the most mysterious and poorly understood planets in our solar system. The poles of Uranus are tipped over by an extraordinary 98º (compared with an obliquity of 23.5º for the Earth) leading to enormous annual variations in solar forcing, with the poles annually receiving more sunlight per unit area than the equator! In contrast, Neptune’s obliquity of 29º appears much less anomalous. The Voyager 2 fly-bys in 1986 and 1989 provided our only close-up views of these worlds and revealed that Uranus is in almost perfect radiative balance with the Sun, while Neptune emits thermally more than 2.5 times the solar radiation it receives! Perhaps as a result of this imbalance, the atmospheric circulation of Uranus was found to be rather quiescent, while that of Neptune was extraordinarily dynamic and active.

More than a quarter of a century later, the spatial resolution of ground-based telescopes has been transformed by the development of adaptive optics. The activity of Uranus’s atmosphere has been seen to increase dramatically through its equinox in 2007, while Neptune’s atmosphere shows enormous changes in cloud activity. We have been monitoring and these developments with an extensive programme of near-infrared ground-based observations at the Gemini-North Telescope in Hawai’i and ESO’s Very Large Telescope in Chile. Near infrared reflectance spectroscopy enables us to determine the vertical and horizontal distribution of cloud and gaseous abundances in these atmospheres, using our world-leading NEMESIS retrieval code. Recent highlights include: 1) the first positive detection of hydrogen sulphide in the atmosphere of Uranus (https://www.ox.ac.uk/news/science-blog/what-do-uranuss-cloud-tops-have-common-rotten-eggs) and probable detection in Neptune’s atmosphere; 2) the first ground-based detection of methane latitudinal variability in Neptune’s atmosphere; and most recently 3) a ‘holistic’ cloud model that matches the observed reflectivity spectra of both Uranus and Neptune from 0.3 to 2.5 microns, and can explain the difference in colour between these two worlds (https://www.ox.ac.uk/news/2022-05-31-scientists-explain-why-uranus-and-neptune-are-different-colours).

The aim of this project is to develop our ground-based visible and near-infrared observing programme and combine these new observations with existing thermal infrared determinations and also with observations now scheduled with the recently launched James Webb Space Telescope. The combination of thermal emission and reflected sunlight observations should enable us to build up a self-consistent picture of the circulation and cloud-forming processes at work on the ice giants during a period of rapid change. This project is particularly timely given that a dedicated space mission to one of the Ice Giants was recommended by the 2022 NASA Decadal Survey in Planetary Science. Hence, the Ice Giants are currently a ‘hot topic’ and the successful candidate would be joining a well-established planetary data analysis group that is actively involved in both observational astronomy and planetary missions.

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

Raymond Pierrehumbert
Project ref: AOPP/RTP/1/

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. I am seeking up to two DPhil (PhD) students for work in the general area of exoplanet climate modeling, with a particular emphasis on smaller planets (super-Earth size and below) which can have a more rich diversity of atmospheric compositions than the hydrogen-dominated gas giants, and offer a range of additional phenomena associated with the possibility of a condensed rocky, icy or liquid surface. In all of our work, there is an emphasis on maintaining an appropriate balance between theoretical work or idealized modeling aimed at elucidating fundamental principles, and work with more comprehensive general circulation models.

Two DPhil (PhD) students are sought for exoclimate projects in one or more of the following general areas: (1) Atmospheric escape and implications for habitability of M-star planets, (2) Baroclinic instability on tide-locked slowly rotating planets (3) Exchange of volatiles between planetary interiors and atmospheres, including effects of magma oceans on atmospheres and implications of the deep carbon cycle and CO2 outgassing on the outer edge of the habitable zone. (4) Transient phenomena in exoplanet atmospheres, their use in constraining planetary characteristics, and prospects for detection with future observational programs. (5) Spatially inhomogeneous chemistry of planetary atmospheres driven by mixing due to idealized large scale flow. In addition to these specific project areas, I am open to suggestions from students who wish to take the initiative in defining their own research direction within the general area of exoplanet climate and climate evolution.

There are also possibilities for DPhil students to work in collaboration with the ERC EXOCONDENSE project on topics related to effect of condensible substances on exoplanet climate dynamics, and on generalised moist convection in planetary atmospheres. Further information on EXOCONDENSE is available here. Topics of interest include both generalized moist convection and its parameterization and condensation effects (including clouds) in planetary scale dynamics. Further information on EXOCONDENSE can be found at the EXOCONDENSE project page.

These projects require 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 projects involve 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.