Probing the origins of planets with the James Webb Space Telescope
In the 2020s, exoplanet studies will move increasingly towards their chemical composition and its origins in protoplanetary disks. Some of the key goals are to link planetary elemental abundances to their formation location and migration history in a disk, and to establish the origins of habitable chemical compositions. The James Webb Space Telescope, due to launch within 1-2 years, is poised to provide a wealth of new spatially and spectrally resolved data on the composition of planet-forming material around young stars on Solar System spatial scales. This has the potential to revolutionise our understanding of planetary origins. Some of the most pressing problems involve the delivery of water to terrestrial planets and the early budget of volatile vs refractory carbon. More generally, questions abound on the detailed budget of volatile and semi-volatile elements, including the bio-essential ones, at the time of incorporation into planets. JWST will help to address these issues by revealing the presence, abundance, and spatial distribution of important gas-phase molecules, ices, and minerals. PhD projects are available to analyse and model the extraordinary upcoming JWST data on protoplanetary environments, and to draw links with the properties of mature planetary systems. You will also have support from a group external to UCL and with complementary expertise, allowing you to build a wide range of skills.
Contact: Dr. Mihkel Kama (m.kama AT ucl.ac.uk)
Spectroscopy of hot rocky Super-Earths
Thousands of exoplanets have been discovered in the recent years, most of them are gas giants and hundreds appear to be rocky (silicate-rich). Many of these exoplanets have very short orbital period, hence hot atmospheres. Some of the rocky super-Earths are evaporating with complex atmospheric compositions. These planets have a lot in common with the young Earth; the massive amounts of water in their atmospheres can melt rocks and put their constituents into the atmosphere. Similar processes are expected in the atmospheres of the post-impact planets.
The atmospheres of hot rocky super-Earths have very different spectroscopic signatures than gas giants or cooler objects, which will influence interpretation of the atmospheric observations. Examples of the recent atmospheric retrievals (e.g. of HD 209458b, GJ 1214b, 55 Cancri e and HD 189733b) show that transit observations can help to establish the bulk composition of a planet. However, it is only with good predictions of likely atmospheric composition allied to a comprehensive database of spectral signatures that the observed spectra can be deciphered. This PhD project will aim to produce a comprehensive library of molecular opacities specific to lava-planets. The results will be incorporated into exoplanet models developed at UCL and made available to the scientific community. These models will enable the interpretation of present and future spectroscopic studies of rocky super-Earths. Exactly these types of hot solid planets will be the likely targets of NASA's JWST or ESA's ARIEL.
Contact: Prof. Sergey Yurchenko (s.yurchenko AT ucl.ac.uk)
Pandemonium in the planetary graveyard
Defying the notion of the silent graveyard, planetary systems refuse to go quietly into the long night. Instead, a significant fraction show one or more signs of dynamical reanimation, with strong indications of general mayhem during the final stages of stellar evolution. These rejuvenated planetary systems manifest as irregular and complex transit events, transient optical emission features, and variable infrared fluxes from dust production and destruction. Ultimately, all leave their detailed chemical signatures on the surface of the white dwarf stars they orbit, and provide powerful insight into the masses and geochemical structures of the planetary bodies. At UCL, we are leading the study of these evolved planetary systems in the infrared via their dusty debris disks, in the optical via transiting events, and in the ultraviolet where elemental abundances can be measured from the polluted stellar surfaces. The project will involve at least two observational approaches, including but not limited to: studies of available transit data, infrared data that track debris disk variability, and importantly bulk compositions for minor and major planetary bodies.
Contact: Prof Jay Farihi (j.farihi AT ucl.ac.uk)
Molecular line lists for characterising extrasolar planets
The number of extrasolar planets detected is increasing rapidly and attention is turning to determining what they are made of. To do this requires very significant quantities of spectroscopic data which is largely unavailable. A major new project is being launched at UCL to calculate a comprehensive set of molecular line lists that will allow scientists to model the atmospheres of hot exoplanets, brown dwarf and cools stars (see www.exomol.com). One (or possibly two) PhD students are sought to work in a team of about 6 people on this project. Interested students should have a good understanding of quantum mechanics and be interested in computational work. The studentships are available to both UK and EU nationals.
Contact: Prof Jonathan Tennyson firstname.lastname@example.org
Unveiling the nature of super-Earths with current and future observatories
Super-Earths, i.e. planets lighter than ten Earth masses, appear to be the most common planets in our galaxy. Being absent in our Solar Systems, their nature is rather mysterious: from their densities we gather there is a large variety of cases, ranging from big rocky planets to small Neptunes or more exotic types. The chemical composition and state of their atmospheres, can be used as a powerful diagnostic of the history, formation mechanisms and evolution of these planets. In the past fifteen years, the UCL exoplanet team led by Prof. Tinetti has worked at the forefront of the spectral/photometric measurements of exoplanet atmospheres and their interpretation, with molecular species being detected in the atmospheres of giant planets and super-Earths (e.g. extremely hot 55 Cnc-e and habitable-zone K2-18b). As part of the PhD, the student will have the opportunity to work in collaboration with Prof. Giovanna Tinetti, Dr. Angelos Tsiaras and Dr. Yuichi Ito on a number of aspects connected with the observations and modelling of super-Earths’ atmospheres with current and future observatories (HST, JWST) and dedicated space missions (ARIEL).
The orbits of charged particles in planetary magnetospheres, and the dynamics of the orbits of stars in galaxies, are the result of how the ‘test particles’ within each system - individual ions / electrons or individual stars - respond to either gravitational or electromagnetic fields. This project is principally a project in planetary plasma physics, but has an 'interdisciplinary element' based on exploring analysis techniques used in other areas of astrophysics, and seeing how they can be applied to model spacecraft magnetic field data which probe the plasma sheet regions of the planets Saturn and Jupiter. The main 'strands' of the project would be:
- Plasma Sheet Modelling: Developing a general magnetic field model associated with the plasma sheet current in planetary magnetospheres - to capture the full complexity of the current sheet, a many-parameter model will be required for fitting spacecraft data. Fitting techniques, based on Monte Carlo and statistical methods, have been used in the areas of stellar orbital dynamics and cosmology. The idea would be to identify the best fitting methods from these domains for adaptation to the 'current sheet' modelling.
- Exploring Representations of Particle Dynamics: This idea is less 'fully formed', so would be a more minor component - but, if successful, would enhance work our group have done in numerically modelling the trajectories of charged particles in planetary magnetic fields of different types. The analogous problem of modelling stellar orbits in a Galaxy often uses concepts from dynamical systems theory, such as 'action integrals' - the analog of 'action integrals' in magnetospheric plasma is associated with adiabatic constants of the particle motion. This more exploratory part of the project would examine whether we could improve the way we represent the motion of large ensembles of trapped particles by applying relevant concepts from dynamical systems theory, as applied to other astrophysical environments.
Contact: Prof Nick Achilleos (nicholas.achilleos AT ucl.ac.uk)