With the end of answer questions as, how common are planetary systems like our own in the Universe? and What is the diversity of planetary systems that we could find in the universe?, we develop a semi-analytical model for computing planetary systems formation and consider different initial conditions for generating a large sample of planetary systems, which is analysed statistically. We explore the effects in the planetary system architecture of assuming different initial disc profiles and planetary migration rates.

GAME (Gravitation Astrometric Measurement Experiment) is a mission concept based on astronomical techniques for high precision measurements of interest to Fundamental Physics and cosmology, in particular the γ and β parameters of the Parameterized Post-Newtonian formulation of gravitation theories extending the General Relativity.

High precision astrometry also provides the light deflection induced by the quadrupole moment of Jupiter and Saturn, and, by high precision determination of the orbits of Mercury and high elongation asteroids, the PPN parameter β.

The astrometric and photometric capabilities of GAME may also provide crucial complementary information on a selected set of known exo-planets.

Thanks to the combination of transit photometry and radial velocity doppler measurements, we are now able to constrain theoretical models of the structure and evolution of objects in the whole mass range between icy giants and stars, including the giant planet/brown dwarf overlapping mass regime (Leconte et al. 2009). In the giant planet mass range, the significant fraction of planets showing a larger radius than predicted by the models suggests that a missing physical mechanism which is either injecting energy in the deep convective zone or reducing the net outward thermal flux is taking place in these objects. Several possibilities have been suggested for such a mechanism:

• • downward transport of kinetic energy originating from strong winds generated at the planet's surface (Showman & Guillot 2002),

• • enhanced opacity sources in hot-Jupiter atmospheres (Burrows et al. 2007),

• • ohmic dissipation in the ionized atmosphere (Batygin & Stevenson 2010),

• • (inefficient) layered or oscillatory convection in the planet's interior (Chabrier & Baraffe 2007),

• • Tidal heating due to circularization of the orbit, as originally suggested by Bodenheimer, Lin & Mardling (2001).

We present the results of detailed simulations of the RV and astrometric signals expected from the Sun, when taking into account its activity (spots, plages, convection). To do so, we considered all structures (2,000,000) identified on the Sun surface over a full cycle. We show that the Sun activity would prevent the detection of the Earth in the Habitable Zone with RV technics with today or future forthcoming instruments, mainly because of inhomogeneous convection. We also show that the activity-induced signal would be comparatively easier for the astrometric detection of the Earth of similar planets.

The microlensing technique has found 10 exoplanets to date and promises to discover more in the near future. While planetary transit light curves all show a familiar shape, planetary perturbations to microlensing light curves can manifest a wide variety of morphologies. We present a graphical guide that may be useful when understanding microlensing events showing planetary caustic perturbations.

We present preliminary results from a study of the variations of the optical spectrum of the Earthshine over a period of a year. Our goal is to follow, on several timescales, the spectral changes of the signature of various biomarkers that are potential indicators of habitability and/or biological activity, and of the Vegetation Red Edge, a feature around 700 nm due to photosynthetic organisms.

Secondary eclipse observations of exoplanets at near-infrared wavelengths are important to constrain the energy budgets of hot-Jupiters, since they probe the radiation from the planet's atmosphere at the peak of the spectral energy distribution. Since this wavelength range is accesible from the ground, we have started the GROUnd-based Secondary Eclipse (GROUSE) project. As part of the GROUSE project, we target a sample of hot-Jupiters at near-infrared and optical wavelengths. Planets include TrES-3b, HAT-P-1, WASP-18b and WASP-33b.

The detection of sodium absorption during primary transit implies the presence of an atmosphere around an extrasolar planet. WASP-17b (Anderson et al. 2010a) is the least dense known planet, with a radius twice that of Jupiter. It orbits an F6-type star, and its low gravity gives its atmosphere a very large scale height. The sodium transit depth is expected to be 4.1 – 5.2 times deeper than for HD 209458b (Seager & Sasselov 2000). We obtained 24 spectra with the GIRAFFE spectrograph on the VLT, 8 during transit. We measured the flux in the sodium doublet at 5889.95 Å and 5895.92 Å using bandpasses 0.75, 1.5, 3.0 and 6.0 Å. We find a transit depth of 0.55±0.13% at 1.5 Å (4.3σ). WASP-17b therefore has an atmosphere which is depleted in sodium compared to predictions.

The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?

In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.

The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.

EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.

ϵ Eridani hosts one known inner planet and an outer Kuiper belt analog. Further, Spitzer/IRS measurements indicate that warm dust is present at distances as close as a few AU from the star. Its origin is puzzling, since an “asteroid belt” that could produce this dust would be unstable because of the inner planet. We tested a hypothesis that the observed warm dust is generated by collisions in the outer belt and is transported inward by P-R drag and strong stellar winds. With numerical simulation we investigated how the dust streams from the outer ring into the inner system, and calculated the thermal emission of the dust. We show that the observed warm dust can indeed stem from the outer belt. Our models reproduce the shape and magnitude of the observed SED from mid-IR to sub-mm wavelengths, as well as the Spitzer/MIPS radial brightness profiles.

There are now more than 35 stars with transiting planets for which the stellar obliquity—or more precisely its sky projection—has been measured, via the eponymous effect of Rossiter and McLaughlin. The history of these measurements is intriguing. For 8 years a case was gradually building that the orbits of hot Jupiters are always well-aligned with the rotation of their parent stars. Then in a sudden reversal, many misaligned systems were found, and it now seems that even retrograde systems are not uncommon. I review the measurement technique underlying these discoveries, the patterns that have emerged from the data, and the implications for theories of planet formation and migration.

Studying the internal structure of exoplanet-host stars compared to that of similar stars without detected planets is particularly important for the understanding of planetary formation. In this framework, asteroseismic studies represent an excellent tool for a better characterization of stars and for a precise determination of the stellar parameters like mass, radius, gravity, effective temperature. The detection of stellar oscillations is obtained with the same instruments as used for the discovery of exoplanets, both from the ground and from space, although the time scales are very different. Here I discuss some details about the characterization of exoplanethost stars from seismology and the importance of the helium and heavy element abundances in this respect.

We present a new formation mechanism to produce short-period Earth-like planets in the late stage of planet formation, through a collision-merger scenario. In this scenario, a planetary embryo is directly thrown into a close-in orbit after a collision with another embryo, and then the larger merged body is seized by the central star as a hot Earth-like planet.

The standard picture of planet formation posits that giant gas planets are over-grown rocky planets massive enough to attract enormous gas atmospheres. It has been shown recently that the opposite point of view is physically plausible: the rocky terrestrial planets are former giant planet embryos dried of their gas “to the bone” by the influences of the parent star. Here we provide a brief overview of this “Tidal Downsizing” hypothesis in the context of the Solar System structure.

Planetary migration provides a theoretical basis for the observed diversity of exoplanetary systems. We demonstrate that dust settling - an inescapable feature of disk evolution - gives even more rapid type I migration by up to a factor of about 2 than occurs in disks with fully mixed dust. On the other hand, type II migration becomes slower by a factor of 2 due to dust settling. This even more problematic type I migration can be resolved by the presence of a dead zone; the inner, high density region of a disk which features a low level of turbulence. We show that enhanced dust settling in the dead zone leaves a dusty wall at its outer edge. Back-heating of the dead zone by this wall produces a positive radial gradient for the disk temperature, which acts as a barrier for type I migration.

Spectral features corresponding to methane and water opacity were reported based on transmission spectroscopy of HD 189733b with Hubble/NICMOS. Recently, these data, and a similar data set for XO-1b, have been reexamined in Gibson et al. (2010), who claim they cannot reliably reproduce prior results. We examine the methods used by the Gibson team and identify two specific issues that could act to increase the formal uncertainties and to create instability in the minimization process. This would also be consistent with the GPA10 finding that they could not identify a way to select among the several instrument models they constructed. In the case of XO-1b, the Gibson team significantly changed the way in which the instrument model is defined (both with respect to the three approaches they used for HD 189733b, and the approach used by previous authors); this change, which omits the effect of the spectrum position on the detector, makes direct intercomparison of results difficult. In the experience of our group, the position of the spectrum on the detector is an important element of the instrument model because of the significant residual structure in the NICMOS spectral flat field. The approach of changing instrument models significantly complicates understanding the data reduction process and interpreting the results. Our team favors establishing a consistent method of handling NICMOS instrument systematic errors and applying it uniformly to data sets.

We carry out a resolution study on the fragmentation boundary of self-gravitating discs. We perform three-dimensional Smoothed Particle Hydrodynamics (SPH) simulations of discs to determine whether the critical value of the cooling timescale in units of the orbital timescale, βcrit, converges with increasing resolution. Using particle numbers ranging from 31,250 to 16 million (the highest resolution simulations to date) we do not find convergence. Instead, fragmentation occurs for longer cooling timescales as the resolution is increased. These results certainly suggest that βcrit is larger than previously thought. However, the absence of convergence also questions whether or not a critical value exists. In light of these results, we caution against using cooling timescale or gravitational stress arguments to deduce whether gravitational instability may or may not have been the formation mechanism for observed planetary systems.

GJ 1214b is one of the first discovered transiting planets having mass (6.55 M⊕) and radius (2.678 R⊕) smaller than Neptune. To account for its low average density (1870 kg m−3), GJ 1214b must have a significant gas component. We use interior structure models to constrain GJ 1214b's gas envelope mass, and to explore the conditions needed to achieve within the planet pressures and temperatures conducive to liquid water. We consider three possible origins for the gas layer: direct accretion of gas from the protoplanetary nebula, sublimation of ices, and outgassing from rocky material. Despite having an equilibrium temperature below 647 K (the critical temperature of water) GJ 1214b does not have liquid water under most conditions we consider. Even if the outer envelope is predominantly sublimated water ice, in our model a low intrinsic planet luminosity (less than 2 TW) is needed for the water envelope to pass through the liquid phase; at higher interior luminosities the outer envelope transitions from a vapor to a super-fluid then to a plasma at successively greater depths.

The algorithm of spectral energy distribution (SED) calculations for protoplanetary disks and central objects is created. The results of SEDs calculations for substars with protoplanetary disks that have a different ages and inclinational angles are discussed.

With over two dozen exoplanet atmospheres observed today, the field of exoplanet atmospheres is solidly established. The highlights of exoplanet atmosphere studies include: detection of molecular spectral features; constraints on atmospheric vertical temperature structure; detection of day-night temperature gradients; and a new numerical approach to atmosphere temperature and abundance retrieval. As hot Jupiter observations and interpretation are maturing, the next frontier is super Earth atmospheres. Theoretical models of super Earth atmospheres are moving forward with observational hopes pinned on the James Webb Space Telescope, scheduled for launch in 2014. Further in the future lies direct imaging attempts to answer the enigmatic and ancient question, “Are we alone?” via atmospheric biosignatures.