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UCL Astrophysics Group

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PhD Projects: Planetary / Exoplanetary Science

Exoplanetary Studies

 

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: Dr. 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: Dr 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 j.tennyson@ucl.ac.uk 

 

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). 

Contact: Prof Giovanna Tinetti (g.tinetti AT ucl.ac.uk, also cc e.dunford AT ucl.ac.uk) 

 

Solar System / Terrestrial Studies

 

Structures and energetics of the auroral upper atmosphere and ionosphere

Space Weather occurs through the coupling of the solar wind with the Earth's magnetosphere, ionosphere and thermosphere. The thermosphere is the last outer layer of the Earth’s atmosphere, in the altitude range 100 – 500 km. Near the magnetic poles it is the source of the aurora, and is the location of the International Space Station and Low Earth Orbiting (LEO) satellites used for Earth observations. The thermosphere includes charged particles that comprise the ionosphere. Consequently strong electric fields and electrical currents flow at these altitudes, which leads to loss of satellite signals, charging of spacecraft, errors in GPS measurements, through to Geomagnetically Induced Currents (GIC) in the ground that can cause electricity grid transformers to overheat. The solar radiation heating and electrical heating of the atmosphere create atmospheric tides and perturbations. Understanding the mechanisms allow us to be able to predict their occurrence, and attempt to mitigate their effects. More recently, there has been strong evidence of coupling from the lower atmosphere weather through to the upper atmosphere, which has led to the development of Whole Atmosphere Models from the ground to the top of the atmosphere.

The Atmospheric Physics Laboratory has a network of Fabry-Perot Interferometers (FPIs) in the auroral region of northern Scandinavia, within the Arctic Circle. We also have two 3D time-dependent global atmospheric circulation models: the Coupled Middle Atmosphere Thermosphere (CMAT2) model and the Coupled Thermosphere Ionosphere Plasmasphere (CTIP) model. The project can be either an experimental project, or modelling study. The instrumental project will involve fieldwork with the FPIs. We also use satellite and ground-based instruments such as the EISCAT and SuperDARN radars, and run model simulations. We work with scientists internationally, and nationally we have on-running collaborations with the Mullard Space Science Laboratory and the UCL Department of Civil, Environmental and Geomatic Engineering using CubeSats to determine atmospheric densities from in-situ measurements of particle and satellite drag; and in a multi-university collaboration with the UK Meteorological Office to develop an operational Whole Atmosphere Model for Space Weather forecasting.

Contact: Dr Anasuya Aruliah (a.aruliah AT ucl.ac.uk)

 

Planetary Plasmas

Magnetospheric / Plasma Projects: Since 2009, our group has extended our modelling expertise out into the magnetospheric region and constructed models of the disc-like, rapidly rotating magnetospheres of Jupiter and Saturn. We have published several studies comparing the Saturn model with observations from the Cassini spacecraft of the planet's magnetic field and plasma environment (including the environment of the moon, Titan). Further comparative studies of this nature are needed - we have also been trying to develop more sophisticated modelling / analysis techniques for using spacecraft data to probe the structure of the magnetospheric current sheets within giant planet magnetospheres. We have led observational and theoretical studies of the magnetospheric boundary, or magnetopause, of Saturn. Thus for someone interested in plasma / magnetospheric physics, there is a variety of options for postgraduate work.

Planetary Atmospheric Modelling: On the modelling side, we have built global models of the thermospheres and ionospheres of Jupiter and Saturn. These have been used in pioneering studies of the effects of auroral precipitation on upper atmospheric flows and planetwide heating processes. Such studies are important for identifying the types of energy inputs required to explain the unusually high temperatures in the upper atmospheres. Planned future work includes more studies of how time variability of the aurora and the magnetospheric conditions affect the atmospheric flows and heating: a key question here is the timescale associated with the atmosphere's response to changes in magnetospheric conditions. We have Co-Investigator involvement with the team who managed the magnetometer aboard the Cassini spacecraft on studies of Saturn's magnetospheric structure, and we envisage that this experience with spacecraft data will provide valuable future inputs and constraints for our own planetary models.

Auroral Physics: The beautiful auroral displays of magnetised planets (such as Earth, Jupiter and Saturn) are the result of powerful global systems of electrical current which flow between their ionospheres and magnetospheres. At the giant planets, rapid rotation plays an important role in the formation of auroral ovals. The Planetary Plasmas group at UCL have a wealth of experience in both observations and modelling of the auroral physics and the global atmospheric flows which arise via the electrodynamic coupling of the planet and its space environment. We have also developed data analysis tools for analysing two-dimensional images of auroral emissions, and detecting different types of auroral features - which is the first step to identifying the physical origin of these emissions.

Contact: Dr Nick Achilleos (nicholas.achilleos AT ucl.ac.uk)