IntroductionOn this page I have tried to outline all of the research topics I am interested in which includes things I am currently working on, and areas I have submitted proposals for funding to work on. Many of the proposals will not get funded-such is life-so the work explained on this page may be `in progress' for quite some time! NONE of this work is performed in isolation and I have also tried to mention every person I work with in a given area. This page, therefore, is almost a memo to my self.... Please read it with this in mind, it will be incomplete and inaccurate!
Primary GoalsMy main goal is to develop a generic suite of tools and theories with which to understand and interpret observations of planetary (and Brown Dwarf) atmospheres both within and without our Solar system. This means, within the same numerical framework, producing a set of models capable of running across a range of complexities and domains. We want to be able to isolate physical processes efficiently, and explore their interaction with the whole atmosphere. An example would be the ability (which we now have) to run 1D radiative-transfer models using/relaxing a range of approximations, or coupling the same model to a full 3D dynamical simulation. It is only by `bracketing' a given problem in terms of sophistication, i.e. having a complex model, and an idealised model, that we can confidently identify the correct process responsible for a given observed phenomena. As such our research goals align very closely with those of the UK Met Office creating a strong collaboration. This project can be separated into sub-areas, which I list below with the main collaborators, in addition to Isabelle Baraffe, Dave Acreman, Chris Smith, James Manners, David Skalid Amundsen, Benjamin Drummond, Pascal Tremblin, Nigel Wood, John Thuburn, David R. Jackson and Martyn Brake, who collaborate on the project as a whole.
Giant Gaseous Bodies.The hypothesis here is that all giant gaseous bodies, which do not support extensive nuclear processes in their interiors, are a continuum of objects separated in the behaviour of their atmospheres only by a set of parameters:
(1) Bulk: rotation rate, gravity, composition (metallicity etc).
(2) Energy: irradiation (external), heating from interior.
(3) Atmospheric: clouds, hazes and aerosols.
`Hot Jupiters' are essentially analogues of Jupiter but orbiting much closer to their parent star (hence strongly irradiated) and rotation much more slowly (as they are expected to be tidally-locked, i.e. a permanent day and night hemisphere). We have already adapted our models to study these extreme objects. We are now working on further adaptations to study `directly imaged planets', being Jupiter analogues at much younger ages, thereby experiencing increased atmospheric heating from the interior. Finally, we are collaborating on a study of Brown Dwarf atmospheres, separated only from Jovian planets, perhaps (this is controversial) by their metallicity (the two regimes certainly overlap in temperature and mass).
This set of objects, chiefly, will allow us to explore, beyond the relatively well understood effects of rotation rate, the effect of the balance of internal to external heating on an atmospheric state. Additionally, as each of these objects often have indications of the presence of clouds, we will be able to study their radiative and dynamical impact across a broad range of atmospheres.
Collaborators: Geoff Vallis, David Sing, Daniel Apai, Sasha Hinkley.
Terrestrial PlanetsAs we discover more terrestrial exoplanets, and adapt Earth-based models to explore these targets, it becomes even more important that we understand the major `tipping points' in the three atmospheres in or close to the nominal Habitable Zone (HZ) in our own Solar System, namely Earth, Mars and Venus. Therefore, we are studying major evolutions in Earth's atmosphere, and performing comparisons with Venus and Mars. to this end we are exploring the `faint young Sun' paradox and future `moist greenhouse' states. The faint young Sun paradox, is that in Earth's ancient history the Sun was much less luminous (up to 20% due to stellar evolution) and 1D models suggest the Earth should have entered a period of glaciation contradicting evidence from the fossil record. Differing atmospheric compositions could cause this, but also recent 3D models have suggested dynamical effects may play role (essentially breaking the zonal symmetry and thereby making 1D models inapplicable). The moist greenhouse effect, is essentially caused by the reverse phenomenon, an increase in Solar luminosity as the Sun expands, at some point the Earth will enter a phase of runaway greenhouse triggered by increasing moisture content in the atmosphere. However, recent 3D models again show significant discrepancy with the body of 1D studies on when this might occur. These two limiting points allow us, essentially, to study the inner and outer edge of the Earth's HZ. Which can be extraoplated to exo-Earths.
We are also attempting to study the causes of difference in liquid water content between Earth, Mars and Venus. Where did the water on Mars and Venus go? It is possible that Venus lost much of its water, during early evolution by either evaporation to space, or absorption into a magma ocean. Mars, on the other hand, may well have huge water reserves frozen at the poles. Understanding the key reasons for this difference is important for extrapolation to the habitability of a given exoplanet.
The key aim is to use these studies to inform studies of the habitability of a given exoplanet, which is currently incredibly difficult to conclude on.
Collaborators: Tim Lenton, Andy Watson, Ramses Ramirez.
Stellar AgesI am still very much involved in a collaboration lead by Tim Naylor and Cameron Bell, working on deriving reliable ages for young stars. The parameter of age, is absolutely critical in constraining theories of star and planet evolution and formation, and it is a devilishly difficult quantity to derive.
Some of this work also includes looking at the effects of stellar/disc interaction with magnetic fields.
Collaborators: Tim Naylor, Cameron Bell, Stuart Littlefair, Darryl Sergison, Jon Rees, Scott Gregory.
Brown Dwarf DiscsI am also, when I have time, slowly trying to advance studies performed with Tim Harries (using his rather excellent monte carlo RT code: TORUS), exploring the effect of accretion and disc presence on the observable quantities of Brown Dwarfs, and the subsequent feedback between BD and disc.
Collaborators: Tim Harries, Matthew Read, Lewis Ireland.