Discovery, characterisation and understanding of extrasolar telluric and ice planets with transits

Until recently, we had only one planetary system, the Solar system, against which to test our ideas of how planets form and evolve. Since the discovery, in 1995, of the first planet found around another normal star, over 200 other extra-solar planets have been discovered, and we are starting to place the Earth and the Solar system in their cosmic context. Exploration to date focussed on gaseous giant planets, but new instruments and space missions now make it possible to detect and study smaller planets, mainly composed of ice or water and rocks, such as Uranus or Neptune-like planets, but also hypothetical very massive rocky planets / 'super Earths' / or planets with a deep surface layer of water / 'ocean planets'. Early results suggest these rock/ice planets are relatively common around Sun-like stars. Detecting them is a major step towards discovering extrasolar planets capable of supporting life, but also teaches us about the way Earth-like planets form. My proposal aims to contribute to all stages of the study of these planets: discovery, characterisation, and understanding. The first step is to discover the planets, for which I use two complementary methods. The radial velocity method measures the reflex motion of the star due to the pull of the planet, and I will pursue it with the advanced spectrographs HARPS and SOPHIE (at ESO in Chile and OHP in France) in collaboration with European astronomers. My main expertise is with the second method, the transit method, which measures the dimming of the star as a planet passes in front of it. I have already participated in the detection of transits for a dozen gaseous giant planets, as well as the only transiting Neptune-mass planet known yet (GJ 436b). I will search for new transiting rock/ice planets in data from the CoRoT space telescope, and for transits of known low-mass planets with small ground-based telescopes. The next step is to measure their properties. Uniquely powerful observations are possible when a planet transits its parent star, or passes behind it on the opposite side of the orbit, which reveal key properties such as mass, radius, bulk composition, and atmospheric temperature. The Hubble Space Telescope (HST) and Spitzer Infrared Space Telescope Facility (SIRTF) have opened up this field in the past few years. I recently led a team, which made the first detection of a high altitude haze in the atmosphere of the giant planet companion to the bright star HD 189733 using the HST, and have similar observations scheduled soon for GJ. Over the next few years, I will continue using space facilities to characterise newly identified low-mass planets. I also intend to use smaller ground-based telescopes to monitor transits of known planets. These time-critical observations are difficult to schedule at normal sites, and Antarctica, with months of uninterrupted darkness, has emerged as a promising alternative. I take part in a project to install a small telescope for transit observations at Dome C on the central Antarctic plateau, where the Exeter Astrophysics Group is already involved with a number of astronomical projects. The ultimate aim of this program is to improve our understanding of the formation, evolution and structure of rock/ice planets, by comparing the numbers and properties of different types of detected planets to what theoretical models predict. This requires accounting not only for what we see, but also for what we miss. I have investigated the biases in commonly used planet detection methods, and the degree of uncertainty on the properties we measure. I have also, with colleagues specialised in modelling stellar structure, started developing structure models for rock/ice planets, which I plan to extend by collaborating with planet formation specialists. I will then apply this to the results of the observational projects mentioned earlier to build up an end-to-end view of the statistical implications of their results.