It has been proposed that Uranus and Neptune originated interior to ∽ 10 AU, as potential gas giant cores which were scattered outward when Jupiter won the race to reach runaway gas accretion. We present further numerical simulations of this scenario, which show that it reproduces the present configuration of the outer Solar System with a high degree of success for a wide range of initial conditions. Also, we show that this mechanism may have simultaneously ejected planets from the asteroid belt.

Diffuse low-mass stars and brown dwarfs coexist with condensed solar-type stars in the embedded stage of a developing open cluster. It is shown by smoothed-particle-hydrodynamics modelling that interactions between stars and protostars leads to disruption of the protostar to form protoplanets that can then be captured by the star.

The general relativistic perturbations of a uniformly rotating and axisymmetric elastic deformable astronomical body in the first post-Newtonian approximation of Einstein's general relativity is discussed in a co-rotating coordinates. The main new results presented here are the post-Newtonian variations of the energy and Euler equation, which at the Newtonian level of accuracy is so called Jeffreys-Vicente equation and it play a fundamental role for the description of global geodynamics in the classical geophysics. Our results will be useful to treat the relativistic nutation and precession of the Earth and other planets.

We consider the formation of planetesimals via gravitational instability. While minimum solar nebula (MSN) models are known to be gravitationally stable, we find that sufficiently metal enriched and/or colder discs can yield planetesimals by the Goldreich-Ward mechanism (GWM). This is because the shear between gas and solids, previously believed to render the GWM ineffective, can only stir a finite amount of solids.

In this contribution, I summarize recent theoretical attempts to understand important diagnostic aspects of close-in extrasolar giant planets, in particular transits and albedos. The potential scientific returns of the anticipated direct detection of “EGPs” in transit and/or in reflection are significant.

About 40% of the extrasolar giant planets discovered so far have orbital distances smaller than 0.2 AU. These “hot Jupiters” are expected to be in synchronous rotation with their star. The ability to measure their radii prompts a careful reexamination of their structure. I show that their atmospheric structure is complex and that thermal balance cannot be achieved through radiation only but must involve heat advection by large-scale circulation. A circulation model inspired from Venus is proposed, involving a relatively strong zonal wind (with a period that can be as short as 1 day). It is shown that even this strong wind is incapable of efficiently redistributing heat from the day side to the night side. Temperature variations of 200 K or more are to be expected, even at pressures as large as 10 bar. As a consequence, clouds should be absent on the day side, allowing more efficient absorption of the stellar light. The global chemical composition of the atmosphere should also be greatly affected by the presence of large temperature variations. Finally, stellar tides may also be important in their ability to deposit heat at levels untouched by stellar radiation, thereby slowing further the cooling of the planets.

Clouds and hazes are important throughout our solar system and in the atmospheres of brown dwarfs and extrasolar giant planets. Among the brown dwarfs, clouds control the colors and spectra of the L-dwarfs; the disappearance of clouds helps herald the arrival of the T-dwarfs. The structure and composition of clouds will be among the first remote-sensing results from the direct detection of extrasolar giant planets.

We present an extension of our equilibrium model, initially applied to 51 Peg b (Goukenleuque et al. 2000), to other irradiated extrasolar planets with different orbital distances (up to 1 AU). The model yields the mean atmospheric thermal structure and predicts the reflected spectral flux as well as the thermal flux emerging from such planets, in the visible and in the infrared wavelength ranges.

We explore the highly speculative idea of Deuterium - Deuterium (D-D) fusion inside Jupiter as an internal heating source. We suggest that D could have been brought deep inside the planet by planetesimals (during the process of planet formation) and deposited through planetesimal/ices vaporization. Here, the general aspects of the model are presented.

Formation of giant planets along the standard model is considered in the innermost region of protoplanetary nebulae where turbulence has already decayed. Preference of quiescent nebulae is discussed. It is shown that if dust material enough to form a core with about ten times Earth mass and the corresponding amount of gas exist in the innermost region, a giant planet with mass somewhat larger than our Jupiter can form there.

As the number of detected extrasolar planetary systems has steadily grown over the past five years, so too has the number of circumstellar disks with resolved images. In this contribution, I take stock of the current inventory of disk images at various wavelengths; summarize the results of a new disk imaging survey conducted with the Hubble Space Telescope; review the major inferences that can be drawn about disk structure from the extant images; and suggest areas for future progress.

We review here the present knowledge on the gaseous phases of debris disks found around MS and old PMS stars, and make an attempt to connect them with planetary system activity.

Using the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope we have conducted a coronagraphic imaging survey of 18 main sequence stars with large infrared excesses, searching for circumstellar dust (debris) in scattered light. Dusty disks with radial and hemispheric brightness anisotropies and complex morphologies, both possibly indicative of dynamical interactions with unseen planetary mass companions, were spatially resolved and imaged around three young (≲ 10Myr old) stars. From these observations we describe the debris systems around: a) HR 4796A (A0V), a 70 AU radius ring less than 14 AU wide with unequal ansal flux densities; b) HD 141569A (Herbig Ae/Be), a 400 AU radius disk with a 40 AU wide gap; and c) TW Hya (K7 T-Tauri), a pole-on circularly symmetric disk with a radial break in its surface density of scattering particles. Additionally, our non-detection of scattered light and high precision photometry of a fourth system of similar age, HD 98800 A/B, coupled with mid and thermal IR measurements, greatly constrain a likely model for the debris about the B component.

Infrared observations of two T Tauri stars, T Tau and SU Aur, were obtained using long-baseline interferometry with the Palomar Testbed Interferometer (PTI). For both sources, the 2.2 micron emission is resolved at PTF's nominal fringe spacing of 4 milliarcsec. Using simple circumstellar material distributions, we find that the infrared emission region is tenths of AU in size. We also compare our results from PTI with accretion disk models inferred from spectral energy distributions.

I discuss protoplanetary disc evolution under the assumption that magnetohydrodynamic turbulence and self-gravity are the sole sources of angular momentum transport. This assumption implies a magnetically layered disc structure which leads to unsteady accretion, and larger disc masses at late epochs. The resulting environment for planet formation and migration differs qualitatively from the highly simplified – almost toy – models often adopted.

A new method to find the density distribution in disks around protostellar objects, based on linear polarization maps, is presented. This method uses the displacement of the polarization null points as a function of wavelength. Variations in optical depth are converted into density variations with opacity tables for dust grains. The method has been applied with five linear polarization maps obtained at different wavelengths of the classical T Tauri star HL Tau. The slope of the density as a function of radius in the disk is compatible with the model of the standard protosolar nebula. The total mass of the disk is compatible with values determined by other methods. Other objects have been analyzed, with similar results, although with a smaller number of wavelength bands.

Further observations of the submillimetre CO lines in 3 Vega-type stars are reported and interpreted for the gas temperatures they imply. Very low gas temperatures (∽15K) are deduced for all three stars, consolidating the suggestion that, if the gas and dust are remnants of the molecular cloud from which the star system formed, then much of the CO in these systems may be locked up in ices on the surfaces of dust grains.

New photometry of main-sequence debris discs has been carried out at 850 and 450/μm; the derived SEDs indicate that the dust can lie in either thin rings or radially-extended discs, as seen directly in the few nearby objects which are resolvable. All such objects are consistent with a long wavelength opacity index β of 1.0±0.2 - similar to T Tauri stars, but significantly lower than embedded objects.

Our efficient numerical approach has been applied to modeling the asymmetric circumstellar dust disk around β Pictoris as observed with the HST/STIS. We present a new model on the origin of the warping of the β Pic disk. We suggest that the observed warp is formed by the gravitational influence of a planet with a mass of about 10 masses of Earth, at a distance of 70 AU, and a small inclination (∽ 2.5°) of the planetary orbit to the main dust disk. Results of our modeling are compared with the STIS observations.

A model with two dust components is used do explain the circumstellar structure of weak-T Tauri stars. The IR-excess was calculated and compared to spectroscopic criteria in order to classify the objects according an evolutionary sequence. About 46% of the sample correspond to young main sequence stars showing dust distribution consistent with a disrupted disk, that could be possibly caused by the formation of a planetary system.